Implement fixed interval refresh task scheduling

[ashking94]

Description

Added fixed interval scheduling capability for refresh tasks to ensure consistent intervals between refreshes. Key changes:

1. Introduced new setting cluster.index.refresh.fixed_interval_scheduling.enabled (default: false)
2. Enhanced AbstractAsyncTask to track last run time and calculate dynamic sleep durations
3. Added staggered start times for initial refreshes to prevent concurrent refreshes across shards

Related Issues

Meta issue: #17776

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 11bc39a: 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?

[github-actions]

❌ Gradle check result for dc2db9f: 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?

[ashking94]

❌ Gradle check result for dc2db9f: 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?

Test Result (1 failure / +1)org.opensearch.wlm.WorkloadManagementIT.testHighCPUInMonitorMode {p0={"search.concurrent_segment_search.enabled":"false"}}
--
[org.opensearch.wlm.WorkloadManagementIT.testHighCPUInMonitorMode {p0={"search.concurrent_segment_search.enabled":"false"}}](https://build.ci.opensearch.org/job/gradle-check/55468/testReport/junit/org.opensearch.wlm/WorkloadManagementIT/testHighCPUInMonitorMode__p0___search_concurrent_segment_search_enabled___false___/)

[github-actions]

✅ Gradle check result for dc2db9f: SUCCESS

[codecov]

Codecov Report

Attention: Patch coverage is 93.10345% with 2 lines in your changes missing coverage. Please review.

Project coverage is 72.36%. Comparing base (8312e42) to head (dc2db9f).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...in/java/org/opensearch/indices/IndicesService.java	75.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #17777      +/-   ##
============================================
- Coverage     72.51%   72.36%   -0.15%     
+ Complexity    66142    66050      -92     
============================================
  Files          5356     5356              
  Lines        306421   306446      +25     
  Branches      44393    44395       +2     
============================================
- Hits         222192   221772     -420     
- Misses        66024    66551     +527     
+ Partials      18205    18123      -82     

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