Adding default use cases

[amitgalitz]

Description

The reason I went with a separate defaults file for now is so we don't make breaking changes on our template if customers gives us feedback for how to this differently.

Some concerns I have:

1. Customers might have a hard time knowing what to substitute, for example if they want to change connector post functions they need to know this key:
   "create_connector.actions.pre_process_function": "<content>"
   or for sparse search: "register_local_sparse_encoding_model.function_name"

2. If we want to make these more flexibly its going to be hard to do substitution on things like the index mapping unless user gives a whole string version of there mapping, settings and alias and we make the entire configuration a substitution.

3. Currently you can see I have two versions of create connector - deploy - register. This is due that some connectors have more optional parameters then the others. One solution is having many files for each variation, another is to potentially have the connectors made with empty fields (for example truncate is only needed in cohere default so if we have that for an OpenAI connector it will just be there and unused).

I only added 3 fully working defaults here for now, will have lots more to add if this approach seems fine. I want to also add a good amount of local models so that at least for fast POC or demo users can have a one click set up of an entire use case with 0 additional input like:

POST /_plugins/_flow_framework/workflow?use_case=local_neural_sparse_search
{}
or
POST /_plugins/_flow_framework/workflow?use_case=local_neural_sparse_search

another example with current use cases in PR:

POST /_plugins/_flow_framework/workflow?use_case=cohere-embedding_model_deploy
{
    "create_connector.credential.key" : "123"
}

Issues Resolved

List any issues this PR will resolve, e.g. Closes [...].

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[codecov]

Codecov Report

Attention: Patch coverage is 56.75676% with 32 lines in your changes are missing coverage. Please review.

Project coverage is 72.15%. Comparing base (1f6573d) to head (cdb6459).

❗ Current head cdb6459 differs from pull request most recent head 80ca636. Consider uploading reports for the commit 80ca636 to get more accurate results

Files	Patch %	Lines
...h/flowframework/rest/RestCreateWorkflowAction.java	17.85%	22 Missing and 1 partial ⚠️
.../org/opensearch/flowframework/util/ParseUtils.java	64.28%	3 Missing and 2 partials ⚠️
...ensearch/flowframework/common/DefaultUseCases.java	92.30%	0 Missing and 2 partials ⚠️
...earch/flowframework/transport/WorkflowRequest.java	66.66%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #583      +/-   ##
============================================
- Coverage     72.55%   72.15%   -0.40%     
- Complexity      659      670      +11     
============================================
  Files            80       81       +1     
  Lines          3399     3462      +63     
  Branches        268      278      +10     
============================================
+ Hits           2466     2498      +32     
- Misses          816      842      +26     
- Partials        117      122       +5     

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[jackiehanyang]

Some nit comments on this draft pr, will review again once the pr is ready for review.

[joshpalis]

Overall looks good to me, thanks @amitgalitz for this, definitely improves ease of use. Just had a few comments

[owaiskazi19]

Have some design questions and code/style comments to discuss. Without a frontend, this functionality might appear somewhat complex to users. However, we are steadily advancing towards enhancing the framework's capabilities.

[owaiskazi19]

Please create those 2 issues to either continue the discussion over the design or have a follow up PR. Rest looks good. Thanks for addressing the comments. @dbwiddis can you take a look and we can merge this in?

[dbwiddis]

LGTM! This is an awesome addition.