Fix DSL router, update UI for query assist

[sejli]

Description

• In this PR, cat.indices is validated to have a format field and index field. Since cat.indices does not require an index field, I changed it to a maybe so that it doesn't break other components that call this API.
• When query assist successfully generates PPL, display a callout.
• Remove return button next to query assist input field.

Screen.Recording.2024-03-22.at.3.17.04.PM.mov

Issues Resolved

N/A

Check List

• New functionality includes testing.
  • All tests pass, including unit test, integration test and doctest
• New functionality has been documented.
  • New functionality has javadoc added
  • New functionality has user manual doc added
• Commits are signed per the DCO using --signoff

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 57.76%. Comparing base (3817476) to head (98fc5f5).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1612   +/-   ##
=======================================
  Coverage   57.75%   57.76%           
=======================================
  Files         367      367           
  Lines       13825    13826    +1     
  Branches     3627     3626    -1     
=======================================
+ Hits         7985     7986    +1     
  Misses       5777     5777           
  Partials       63       63           

Flag	Coverage Δ
dashboards-observability	57.76% <100.00%> (+<0.01%)	⬆️

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