[FEATURE] Improved Documentation for Index Transforms

[sarthakaggarwal97]

Is your feature request related to a problem?
There is not enough documentation for transform job in OpenSearch. While it enumerates the purpose and the APIs of Index Transform, there is a scope of improvement over here.

Things to be covered in documentation

1. Index Transforms as ISM Action
2. Transform Index Settings
3. Transform Phases
4. Transform Metadata and Configurations

What solution would you like?
We should consider adding elaborate documentation to enable and make the users aware of the capabilities of a transform job.

[dblock]

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