Add new extensible method to DocRequest to specify type

[cwperks]

Description

This PR adds a new extensible method to DocRequest to specify type. By itself, this PR is not very interest in the core as all DocRequest would be of type indices. The point of this PR is that this would be an extension point for plugins to start categorizing requests into buckets that have meaning to their use-case.

The javadoc introduced in this PR brings up a use-case in the reporting plugin that would create REST APIs and corresponding transport actions for actions that pertain to a single report definitions such as creating a report definition, editing the definition, deleting it or getting it. In such cases, this method can be overridden to specify the type. When the security plugin is installed and resource sharing + authorization is used, this type would be used in the authorization process to figure out what actions the current user is allowed to perform on the single resource give its identifier (DocID). Without a change like this, it would need to be assumed that a single resource system index contains a single type of resource. This change would further allow multiple resource types to live in the same index (i.e. saved objects in dashboards).

Related Issues

Related to opensearch-project/security#4500

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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[github-actions]

❌ Gradle check result for cb7692d: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[owaiskazi19]

Should be good in terms of bwc as well since it's a default method

[github-actions]

✅ Gradle check result for cb7692d: SUCCESS

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 72.84%. Comparing base (01b34a8) to head (cb7692d).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...rc/main/java/org/opensearch/action/DocRequest.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #19313      +/-   ##
============================================
- Coverage     72.87%   72.84%   -0.03%     
+ Complexity    69796    69775      -21     
============================================
  Files          5672     5673       +1     
  Lines        320710   320711       +1     
  Branches      46360    46360              
============================================
- Hits         233704   233610      -94     
- Misses        68111    68201      +90     
- Partials      18895    18900       +5     

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