Auto Swagger Doc Generation

[alexanderbez]

This PR starts the groundwork for the automatic generation of REST (Swagger) docs using https://github.com/swaggo/swag.

So far the PR adds annotated documentation to a single handler BroadcastTxRequest and mounts the docs at /swager/.

To Do:

• Add docs on docs
• Finish and test remaining handlers
  • x/gov
  • x/auth
  • x/bank
  • x/slashing
  • x/staking
  • x/supply
  • x/mint
  • x/genutil
  • x/distribution
  • client/rpc

closes: #2179

/cc @jackzampolin @tnachen @faboweb @marbar3778

---

• 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.

• Wrote tests

• Updated relevant documentation (docs/)

• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md

• Re-reviewed Files changed in the github PR explorer

---

For Admin Use:

• Added appropriate labels to PR (ex. wip, ready-for-review, docs)
• Reviewers Assigned
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)

[codecov]

Codecov Report

Merging #5038 into master will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #5038      +/-   ##
==========================================
+ Coverage   55.04%   55.06%   +0.01%     
==========================================
  Files         291      291              
  Lines       17835    17835              
==========================================
+ Hits         9818     9820       +2     
+ Misses       7310     7308       -2     
  Partials      707      707

[alexanderbez]

@marbar3778 only in auth :)

[alexanderbez]

Looks to be an issue somewhere in the annotations as upgrading the docs yields different results each time.

[alexanderbez]

Punting this from 0.38 to 0.39

[tac0turtle]

@alexanderbez should we close this since we will be doing client work with grpc and can generate the swagger docs from there?