Add boolean parameter to the ISM rollover action that prevents rollover on empty indices

[tandonks]

Description

Adds a new prevent_empty_rollover parameter to the ISM rollover action that prevents rolling over indices with zero documents, addressing a critical user pain point where empty indices continuously roll over due to OR-based condition semantics.

Introduces an optional prevent_empty_rollover boolean parameter that checks document count before evaluating other rollover conditions:

{
  "rollover": {
    "min_index_age": "7d",
    "min_size": "50gb",
    "prevent_empty_rollover": true
  }
}

When prevent_empty_rollover: true:

• Rollover is prevented if doc_count = 0
• Step status returns CONDITION_NOT_MET (retries not consumed)
• Rollover proceeds normally once documents are added
• Existing OR behavior unchanged for non-empty indices

Related Issues

Resolves #1541

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 95.23810% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 76.17%. Comparing base (0063142) to head (2c75593).

Files with missing lines	Patch %	Lines
...atemanagement/step/rollover/AttemptRolloverStep.kt	92.30%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1542      +/-   ##
==========================================
+ Coverage   76.15%   76.17%   +0.02%     
==========================================
  Files         375      375              
  Lines       17569    17588      +19     
  Branches     2411     2415       +4     
==========================================
+ Hits        13379    13397      +18     
- Misses       2948     2952       +4     
+ Partials     1242     1239       -3     

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[shiv0408]

Should we not have a version check here for backward compatibility?

[tandonks]

Ohh right, thanks for catching this, let me make the change

[shiv0408]

Thanks for making this change @tandonks, I just have one comment regarding backward compatibility. Please check if that change is required.

[tandonks]

I had raised the PR from main rather than fork, so shifting it to new #1545