.Net: Ensure Action is JSON format in Stepwise Planner (#1976)

### Motivation and Context
Sometimes, the LLM populates the [ACTION] with non-JSON data. To
mitigate this from happening, this PR updates the labels for the
[ACTION] section of the prompt to more explicitly state that **_only_**
JSON should be written there.

### Description
- [ACTION] has been changed to [JSON ACTION] in the prompt to make it
clear that JSON should appear in this section.
- $JSON_BLOB has been changed to $JSON_ACTION to make it more clear that
the instructions above are for the [JSON ACTION] section

### Contribution Checklist
- [x] The code builds clean without any errors or warnings
- [x] The PR follows SK Contribution Guidelines
(https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
- [x] The code follows the .NET coding conventions
(https://learn.microsoft.com/dotnet/csharp/fundamentals/coding-style/coding-conventions)
verified with `dotnet format`
- [x] All unit tests pass, and I have added new tests where possible
- [x] I didn't break anyone 😄

---------

Co-authored-by: Gina Triolo <51341242+gitri-ms@users.noreply.github.com>
Co-authored-by: Dmytro Struk <13853051+dmytrostruk@users.noreply.github.com>

dotnet/src/Extensions/Extensions.UnitTests/Planning/StepwisePlanner/ParseResultTests.cs

@@ -35,9 +35,9 @@ public void WhenInputIsFinalAnswerReturnsFinalAnswer(string input, string expect
     }
 
     [Theory]
-    [InlineData("To answer the first part of the question, I need to search for Leo DiCaprio's girlfriend on the web. To answer the second part, I need to find her current age and use a calculator to raise it to the 0.43 power.\n[ACTION]\n{\n  \"action\": \"Search\",\n  \"action_variables\": {\"input\": \"Leo DiCaprio's girlfriend\"}\n}", "Search", "input", "Leo DiCaprio's girlfriend")]
-    [InlineData("To answer the first part of the question, I need to search the web for Leo DiCaprio's girlfriend. To answer the second part, I need to find her current age and use the calculator tool to raise it to the 0.43 power.\n[ACTION]\n```\n{\n  \"action\": \"Search\",\n  \"action_variables\": {\"input\": \"Leo DiCaprio's girlfriend\"}\n}\n```", "Search", "input", "Leo DiCaprio's girlfriend")]
-    [InlineData("The web search result is a snippet from a Wikipedia article that says Leo DiCaprio's girlfriend is Camila Morrone, an Argentine-American model and actress. I need to find out her current age, which might be in the same article or another source. I can use the WebSearch.Search function again to search for her name and age.\n\n[ACTION] {\n  \"action\": \"WebSearch.Search\",\n \"action_variables\": {\"input\": \"Camila Morrone age\", \"count\": \"1\"}\n}", "WebSearch.Search", "input",
+    [InlineData("To answer the first part of the question, I need to search for Leo DiCaprio's girlfriend on the web. To answer the second part, I need to find her current age and use a calculator to raise it to the 0.43 power.\n[JSON ACTION]\n{\n  \"action\": \"Search\",\n  \"action_variables\": {\"input\": \"Leo DiCaprio's girlfriend\"}\n}", "Search", "input", "Leo DiCaprio's girlfriend")]
+    [InlineData("To answer the first part of the question, I need to search the web for Leo DiCaprio's girlfriend. To answer the second part, I need to find her current age and use the calculator tool to raise it to the 0.43 power.\n[JSON ACTION]\n```\n{\n  \"action\": \"Search\",\n  \"action_variables\": {\"input\": \"Leo DiCaprio's girlfriend\"}\n}\n```", "Search", "input", "Leo DiCaprio's girlfriend")]
+    [InlineData("The web search result is a snippet from a Wikipedia article that says Leo DiCaprio's girlfriend is Camila Morrone, an Argentine-American model and actress. I need to find out her current age, which might be in the same article or another source. I can use the WebSearch.Search function again to search for her name and age.\n\n[JSON ACTION] {\n  \"action\": \"WebSearch.Search\",\n \"action_variables\": {\"input\": \"Camila Morrone age\", \"count\": \"1\"}\n}", "WebSearch.Search", "input",
         "Camila Morrone age", "count", "1")]
     public void ParseActionReturnsAction(string input, string expectedAction, params string[] expectedVariables)
     {

dotnet/src/Extensions/Planning.StepwisePlanner/Skills/StepwiseStep/skprompt.txt

@@ -15,10 +15,10 @@ To use the functions, specify a JSON blob representing an action. The JSON blob
 Do not call functions directly; they must be invoked through an action.
 The "action_variables" value should always include an "input" key, even if the input value is empty. Additional keys in the "action_variables" value should match the defined [PARAMETERS] of the named "action" in [AVAILABLE FUNCTIONS].
 Dictionary values in "action_variables" must be strings and represent the actual values to be passed to the function.
-Ensure that the $JSON_BLOB contains only a SINGLE action; do NOT return multiple actions.
+Ensure that the $JSON_ACTION contains only a SINGLE action; do NOT return multiple actions.
 IMPORTANT: Use only the available functions listed in the [AVAILABLE FUNCTIONS] section. Do not attempt to use any other functions that are not specified.
 
-Here is an example of a valid $JSON_BLOB:
+Here is an example of a valid $JSON_ACTION:
 {
   "action": "FUNCTION.NAME",
   "action_variables": {"INPUT": "some input", "PARAMETER_NAME": "some value", "PARAMETER_NAME_2": "42"}
@@ -27,12 +27,11 @@ Here is an example of a valid $JSON_BLOB:
 [END INSTRUCTION]
 
 [THOUGHT PROCESS]
-[QUESTION]
-the input question I must answer
+[QUESTION] the input question I must answer
 [THOUGHT]
 To solve this problem, I should carefully analyze the given question and identify the necessary steps. Any facts I discover earlier in my thought process should be repeated here to keep them readily available.
-[ACTION]
-$JSON_BLOB
+[JSON ACTION]
+$JSON_ACTION
 [OBSERVATION]
 The result of the action will be provided here.
 ... (These Thought/Action/Observation can repeat until the final answer is reached.)

dotnet/src/Extensions/Planning.StepwisePlanner/StepwisePlanner.cs

@@ -454,7 +454,7 @@ private static string ToFullyQualifiedName(FunctionView function)
     /// <summary>
     /// The Action tag
     /// </summary>
-    private const string Action = "[ACTION]";
+    private const string Action = "[JSON ACTION]";
 
     /// <summary>
     /// The Thought tag
@@ -474,12 +474,12 @@ private static string ToFullyQualifiedName(FunctionView function)
     /// <summary>
     /// The regex for parsing the action response
     /// </summary>
-    private static readonly Regex s_actionRegex = new(@"\[ACTION\][^{}]*({(?:[^{}]*{[^{}]*})*[^{}]*})", RegexOptions.Singleline);
+    private static readonly Regex s_actionRegex = new(@"\[JSON ACTION\][^{}]*({(?:[^{}]*{[^{}]*})*[^{}]*})", RegexOptions.Singleline);
 
     /// <summary>
     /// The regex for parsing the thought response
     /// </summary>
-    private static readonly Regex s_thoughtRegex = new(@"(\[THOUGHT\])?(?<thought>.+?)(?=\[ACTION\]|$)", RegexOptions.Singleline);
+    private static readonly Regex s_thoughtRegex = new(@"(\[THOUGHT\])?(?<thought>.+?)(?=\[JSON ACTION\]|$)", RegexOptions.Singleline);
 
     /// <summary>
     /// The regex for parsing the final answer response