Allow JSON input for proof specs in tendermint client

[AdityaSripal]

Description

closes: #6431

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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

[codecov]

Codecov Report

Merging #6506 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #6506   +/-   ##
=======================================
  Coverage   56.34%   56.34%           
=======================================
  Files         470      470           
  Lines       28232    28232           
=======================================
  Hits        15907    15907           
  Misses      11200    11200           
  Partials     1125     1125