Mark legacy REST swagger APIs as deprecated

[anilcse]

Description

ref: #7246 (review)

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Before we can merge this PR, please make sure that all the following items have been
checked off. If any of the checklist items are not applicable, please leave them but
write a little note why.

• Targeted PR against correct branch (see CONTRIBUTING.md)
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the module structure standards.
• Wrote unit and integration tests
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• Added relevant godoc comments.
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer
• Review Codecov Report in the comment section below once CI passes

[codecov]

Codecov Report

Merging #7399 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #7399   +/-   ##
=======================================
  Coverage   55.35%   55.35%           
=======================================
  Files         587      587           
  Lines       36469    36469           
=======================================
  Hits        20189    20189           
  Misses      14192    14192           
  Partials     2088     2088