Add target_index_settings to rollup specification

[MrChaos1993]

Description

Allow to create index with specified settings during rollup

Issues Resolved

opensearch-project/index-management#1376

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[dblock]

@MrChaos1993 amend your commit with -s to pass DCO

Exercise an API in a test that returns this data, see https://github.com/opensearch-project/opensearch-api-specification/blob/main/TESTING_GUIDE.md

[github-actions]

Changes Analysis

Commit SHA: 2ef7740
Comparing To SHA: 5ed668d

API Changes

Summary

└─┬Components
  └─┬rollups._common___Rollup
    └──[➕] properties (60999:9)

Document Element	Total Changes	Breaking Changes
components	1	0

• Total Changes: 1
• Additions: 1

Report

The full API changes report is available at: https://github.com/opensearch-project/opensearch-api-specification/actions/runs/13521033472/artifacts/2650104708

API Coverage

	Before	After	Δ
Covered (%)	663 (64.94 %)	663 (64.94 %)	0 (0 %)
Uncovered (%)	358 (35.06 %)	358 (35.06 %)	0 (0 %)
Unknown	45	45	0

[nhtruong]

Test suites that involve the new test failed with Expected status 201, but received 400: application/json. Invalid field [target_index_settings] found in Rollup.

Don't forget to add a line in the CHANGELOG.md describing the change from this PR.