[Star tree] Changes to handle derived metrics such as avg as part of star tree mapping

[bharath-techie]

Description

This PR contains the following changes :

1. Makes 'avg' as derived metric of 'sum' and 'avg'
2. If all base metrics are present, derived metric gets automatically added to mapping
3. Modifying the default metrics to 'sum' and 'count' and by extension 'avg'

Related Issues

Resolves #15148

Check List

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

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[github-actions]

✅ Gradle check result for e09106d: SUCCESS

[codecov]

Codecov Report

Attention: Patch coverage is 91.17647% with 3 lines in your changes missing coverage. Please review.

Project coverage is 71.80%. Comparing base (ed65482) to head (5ec212d).
Report is 16 commits behind head on main.

Files	Patch %	Lines
...va/org/opensearch/index/mapper/StarTreeMapper.java	91.30%	1 Missing and 1 partial ⚠️
...arch/index/compositeindex/datacube/MetricStat.java	83.33%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #15152      +/-   ##
============================================
- Coverage     71.96%   71.80%   -0.16%     
+ Complexity    63304    63165     -139     
============================================
  Files          5219     5219              
  Lines        296033   296052      +19     
  Branches      42756    42763       +7     
============================================
- Hits         213026   212587     -439     
- Misses        65520    65974     +454     
- Partials      17487    17491       +4     

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[github-actions]

❕ Gradle check result for 1052ead: UNSTABLE

Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[github-actions]

✅ Gradle check result for 136ab7c: SUCCESS

[github-actions]

❌ Gradle check result for 35ab173: 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 5ec212d: SUCCESS

[opensearch-trigger-bot]

The backport to 2.x failed:

The process '/usr/bin/git' failed with exit code 128

To backport manually, run these commands in your terminal:

# Navigate to the root of your repository
cd $(git rev-parse --show-toplevel)
# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add ../.worktrees/OpenSearch/backport-2.x 2.x
# Navigate to the new working tree
pushd ../.worktrees/OpenSearch/backport-2.x
# Create a new branch
git switch --create backport/backport-15152-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 dac646011f6c630f291fd10c1609dc3206480943
# Push it to GitHub
git push --set-upstream origin backport/backport-15152-to-2.x
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/OpenSearch/backport-2.x

Then, create a pull request where the base branch is 2.x and the compare/head branch is backport/backport-15152-to-2.x.