fix(proto): install of protoc-gen-gocosmos

[tbruyelle]

Description

Closes: #40

By using go install instead of go get ...@latest, we ensure that the version of protoc-gen-gocosmos matches the version in the go.mod.

---

Author Checklist

All items are required. Please add a note to the item if the item is not applicable and
please add links to any relevant follow up issues.

I have...

• Included the correct type prefix in the PR title
• Added ! to the type prefix if API, client, or state breaking change (i.e., requires minor or major version bump)
• Targeted the correct branch (see PR Targeting)
• Provided a link to the relevant issue or specification
• Followed the guidelines for building SDK modules
• Included the necessary unit and integration tests
• Added a changelog entry in .changelog (for details, see contributing guidelines)
• Included comments for documenting Go code
• Updated the relevant documentation or specification
• Reviewed "Files changed" and left comments if necessary
• Confirmed all CI checks have passed

Reviewers Checklist

All items are required. Please add a note if the item is not applicable and please add
your handle next to the items reviewed if you only reviewed selected items.

I have...

• confirmed the correct type prefix in the PR title
• confirmed ! in the type prefix if API or client breaking change
• confirmed all author checklist items have been addressed
• reviewed state machine logic
• reviewed API design and naming
• reviewed documentation is accurate
• reviewed tests and test coverage