[FEATURE] Rename indices to indexes

[kamingleung]

Is your feature request related to a problem?
Replace any references of indices to indexes on the Index Management UI to align with OpenSearch documentation and writing style.

Areas and underlaying flows that need renaming:

• State management policies
• Policy managed indices
• Indices
• Rollup jobs
• Transform jobs

For example:

[kamingleung]

@praveensameneni @AWSHurneyt Is this something we can look into for 2.9?

[AWSHurneyt]

CC: @getsaurabh02

[MansiShinde]

Hi @bowenlan-amzn, can you assign me this issue?