Make LockService an interface and replace usages of ThreadContext.stashContext

[cwperks]

Description

This PR removes direct usages of ThreadContext.stashContext and implements a new extension point in core (IdentityAwarePlugin) which assigns this plugin a subject to use for the purposes of executing transport actions outside of the authenticated user context.

With this subject, job-scheduler is permitted to access its own system indices without having to use ThreadContext.stashContext explicitly.

This PR also updates the sample plugin to enable testing with Security.

You can test with security in the sample plugin using a command like this:

./gradlew :opensearch-job-scheduler-sample-extension:integTest -Dhttps=true -Dsecurity.enabled=true  -Dtests.opensearch.secure=true -Dtests.opensearch.username=admin -Dtests.opensearch.password=admin -Duser=admin -Dpassword=admin --tests 'SampleJobRunnerRestIT' -i

Related Issues

Resolves opensearch-project/opensearch-plugins#238

Check List

• New functionality includes testing.
• New functionality has been documented.
• API changes companion pull request created.
• Commits are signed per the DCO using --signoff.
• Public documentation issue/PR created.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
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[codecov]

Codecov Report

❌ Patch coverage is 67.32026% with 100 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.48%. Comparing base (8b2c5fa) to head (3e0913c).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
...opensearch/jobscheduler/utils/LockServiceImpl.java	70.10%	41 Missing and 14 partials ⚠️
...obscheduler/rest/action/RestReleaseLockAction.java	0.00%	25 Missing ⚠️
...r/transport/action/TransportGetAllLocksAction.java	80.95%	7 Missing and 1 partial ⚠️
...ensearch/jobscheduler/utils/JobHistoryService.java	80.64%	4 Missing and 2 partials ⚠️
...pensearch/jobscheduler/transport/PluginClient.java	68.75%	4 Missing and 1 partial ⚠️
...rg/opensearch/jobscheduler/JobSchedulerPlugin.java	87.50%	0 Missing and 1 partial ⚠️

❌ Your project status has failed because the head coverage (70.48%) is below the target coverage (75.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #714      +/-   ##
==========================================
+ Coverage   69.99%   70.48%   +0.48%     
==========================================
  Files          38       41       +3     
  Lines        1733     2053     +320     
  Branches      156      165       +9     
==========================================
+ Hits         1213     1447     +234     
- Misses        430      495      +65     
- Partials       90      111      +21     

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