Roll back default language version from 11 to 10 (#799)

### Motivation and Context
C# 11 requires .NET 7+ and we would like to keep the requirement at .NET
6 for now.

- includes a minor cosmetic cleanup for the user-agent name in example
21

dotnet/Directory.Build.props

@@ -6,7 +6,7 @@
     <AnalysisMode>AllEnabledByDefault</AnalysisMode>
     <AnalysisLevel>latest</AnalysisLevel>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
-    <LangVersion>11</LangVersion>
+    <LangVersion>10</LangVersion>
     <Nullable>enable</Nullable>
     <ImplicitUsings>disable</ImplicitUsings>
   </PropertyGroup>

dotnet/src/Extensions/Planning.ActionPlanner/ActionPlanner.cs

@@ -166,33 +166,33 @@ public string ListOfFunctions(string goal, SKContext context)
     [SKFunctionInput(Description = "The current goal processed by the planner", DefaultValue = "")]
     public string GoodExamples(string goal, SKContext context)
     {
-        return """
+        return @"
 [EXAMPLE]
 - List of functions:
 // Read a file.
 FileIOSkill.ReadAsync
-Parameter "path": Source file.
+Parameter ""path"": Source file.
 // Write a file.
 FileIOSkill.WriteAsync
-Parameter "path": Destination file.
-Parameter "content": File content.
+Parameter ""path"": Destination file.
+Parameter ""content"": File content.
 // Get the current time.
 TimeSkill.Time
 No parameters.
 // Makes a POST request to a uri.
 HttpSkill.PostAsync
-Parameter "body": The body of the request.
+Parameter ""body"": The body of the request.
 - End list of functions.
-Goal: create a file called "something.txt".
-{"plan":{
-"rationale": "the list contains a function that allows to create files",
-"function": "FileIOSkill.WriteAsync",
-"parameters": {
-"path": "something.txt",
-"content": null
+Goal: create a file called ""something.txt"".
+{""plan"":{
+""rationale"": ""the list contains a function that allows to create files"",
+""function"": ""FileIOSkill.WriteAsync"",
+""parameters"": {
+""path"": ""something.txt"",
+""content"": null
 }}}
 #END-OF-PLAN
-""";
+";
     }
 
     // TODO: generate string programmatically
@@ -201,31 +201,31 @@ No parameters.
     [SKFunctionInput(Description = "The current goal processed by the planner", DefaultValue = "")]
     public string EdgeCaseExamples(string goal, SKContext context)
     {
-        return """
+        return @"
 [EXAMPLE]
 - List of functions:
 // Get the current time.
 TimeSkill.Time
 No parameters.
 // Write a file.
 FileIOSkill.WriteAsync
-Parameter "path": Destination file.
-Parameter "content": File content.
+Parameter ""path"": Destination file.
+Parameter ""content"": File content.
 // Makes a POST request to a uri.
 HttpSkill.PostAsync
-Parameter "body": The body of the request.
+Parameter ""body"": The body of the request.
 // Read a file.
 FileIOSkill.ReadAsync
-Parameter "path": Source file.
+Parameter ""path"": Source file.
 - End list of functions.
 Goal: tell me a joke.
-{"plan":{
-"rationale": "the list does not contain functions to tell jokes or something funny",
-"function": "",
-"parameters": {
+{""plan"":{
+""rationale"": ""the list does not contain functions to tell jokes or something funny"",
+""function"": """",
+""parameters"": {
 }}}
 #END-OF-PLAN
-""";
+";
     }
 
     private void PopulateList(StringBuilder list, IDictionary<string, List<FunctionView>> functions)

samples/dotnet/KernelHttpServer/KernelHttpServer.csproj

@@ -10,7 +10,6 @@
     <TargetFramework>net6.0</TargetFramework>
     <AzureFunctionsVersion>v4</AzureFunctionsVersion>
     <OutputType>Exe</OutputType>
-    <LangVersion>10</LangVersion>
     <Nullable>enable</Nullable>
     <ImplicitUsings>disable</ImplicitUsings>
     <IsPackable>false</IsPackable>

samples/dotnet/kernel-syntax-examples/Example21_ChatGPTPlugins.cs

@@ -19,7 +19,7 @@ private static async Task RunChatGptPluginAsync()
     {
         var kernel = new KernelBuilder().WithLogger(ConsoleLogger.Log).Build();
         using HttpClient importHttpClient = new HttpClient();
-        importHttpClient.DefaultRequestHeaders.Add("User-Agent", "Microsoft.SemanticKernel");
+        importHttpClient.DefaultRequestHeaders.Add("User-Agent", "Microsoft-Semantic-Kernel");
 
         //Import a ChatGPT plugin using one of the following Kernel extension methods
         //kernel.ImportChatGptPluginSkillFromResourceAsync