GRPC querier init and bank

[aaronc]

ref: #5921

Initial scaffolding for GRPC queries as specified in ADR 021 (#5894) plus x/bank migration as an example case.

Replaces #5882.

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For contributor use:

• 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

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For admin use:

• Added appropriate labels to PR (ex. WIP, R4R, docs, etc)
• Reviewers assigned
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)

[codecov]

Codecov Report

Merging #5953 into master will decrease coverage by 4.79%.
The diff coverage is 28.57%.

@@            Coverage Diff             @@
##           master    #5953      +/-   ##
==========================================
- Coverage   55.70%   50.90%   -4.80%     
==========================================
  Files         446      189     -257     
  Lines       26934    11656   -15278     
==========================================
- Hits        15004     5934    -9070     
+ Misses      10859     5335    -5524     
+ Partials     1071      387     -684     

[aaronc]

Replaced by #6325, #6326, #6335, #6336, #6342, #6343, #6353, and #6367.