[DOC] Add ism.rollup.target_index_settings documentation

[MrChaos1993]

What do you want to do?

• Request a change to existing documentation
• Add new documentation
• Report a technical problem with the documentation
• Other

Tell us about your request. Provide a summary of the request.
In index-management plugin was added new field target_index_settings for rollup job. It allows to create index with specified settings during rollup.

Version: List the OpenSearch version to which this issue applies, e.g. 2.14, 2.12--2.14, or all.

What other resources are available? Provide links to related issues, POCs, steps for testing, etc.
opensearch-project/index-management#1376