docs: address issue and some rephrases in the TopicControl deployment page

[miyoungc]

Description

• Doc update for clarifying that TopicControl only exposes to chat/completion
• Other doc improvements

Checklist

• I've read the CONTRIBUTING guidelines.
• I've updated the documentation if applicable.
• I've added tests if applicable.
• @mentions of the person or team responsible for reviewing proposed changes.

[github-actions]

Documentation preview

https://nvidia.github.io/NeMo-Guardrails/review/pr-1251

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69.51%. Comparing base (78e2069) to head (2d5ac74).
Report is 12 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1251      +/-   ##
===========================================
+ Coverage    68.65%   69.51%   +0.86%     
===========================================
  Files          161      161              
  Lines        15978    16013      +35     
===========================================
+ Hits         10969    11132     +163     
+ Misses        5009     4881     -128     

Flag	Coverage Δ
python	69.51% <ø> (+0.86%)	⬆️

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see 9 files with indirect coverage changes

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[Pouyanpi]

Thank you @miyoungc 👍🏻