x/mint: gRPC query service

[atheeshp]

Description

ref: #5921

closes: #XXXX

---

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 #6535 into master will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #6535      +/-   ##
==========================================
+ Coverage   57.72%   57.74%   +0.02%     
==========================================
  Files         494      495       +1     
  Lines       29644    29656      +12     
==========================================
+ Hits        17111    17125      +14     
+ Misses      11301    11300       -1     
+ Partials     1232     1231       -1     

[alexanderbez]

utACK

[fedekunze]

LGTM. It'd be nice if we could use the existing testing suite for the setup

[amaury1093]

lgtm 👍, just some docs update