Migrate upgrade module to protobuf

[aaronc]

Description

Migrates x/upgrade to support protobuf encoding.

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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 #5659 into master will decrease coverage by 0.65%.
The diff coverage is 1.15%.

@@            Coverage Diff             @@
##           master    #5659      +/-   ##
==========================================
- Coverage   36.12%   35.46%   -0.66%     
==========================================
  Files         330      331       +1     
  Lines       31976    32581     +605     
==========================================
+ Hits        11550    11556       +6     
- Misses      19203    19802     +599     
  Partials     1223     1223

Impacted Files	Coverage Δ
x/upgrade/types/keys.go	0% <ø> (ø)
x/upgrade/types/plan.go	88.88% <ø> (ø)
x/upgrade/types/querier.go	0% <ø> (ø)
x/upgrade/types/proposal.go	82.35% <ø> (ø)
x/upgrade/types/codec.go	100% <ø> (ø)
x/upgrade/types/types.pb.go	0.99% <0.99%> (ø)
simapp/app.go	89.1% <100%> (ø)	⬆️

[alexanderbez]

ACK -- Thank @aaronc! A few minor things:

1. Use appCodec in simapp now.
2. Address changelog merge conflict
3. Remove use of internal/ pkg (just bump the directory up to the parent; ref: Remove Internal from Module Spec + Update Modules #5646)

[alexanderbez]

ACK 🌮 there are just a few minor linting/formatting issues.

[aaronc]

@alexanderbez I think I took care of most of the issues. I'm a bit confused by a couple of golangcibot's recommendations for the CLI package as those imports do appear to be needed.

[aaronc]

Looks like there are a few minor formatting things. Will take a look. And something is weird with CircleCI proto.

[alexanderbez]

proto-breaking doesn't work with PRs that are created from different remotes (i.e. forks). Not sure how to get this working. I need to ask in the Buf repo how to do this.

[alexanderbez]

ACK