Protobuf Encoding Migration

[alexanderbez]

This PR defines the basis of work for migration from Amino to full protobuf encoding. It includes:

• Cleaning up/restructure of Makefile(s)
• Addition of buf tooling
• Migrating /types to protobuf
  • Coin
  • DecCoin
  • Implement CustomProtoType for Int and Uint (to allow gogo proto's customtype)
• CI updates (TODO)

closes: #5444

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For contributor use:

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• 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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