feat: add Licensei

[csatib02]

Overview

• Added makefile target for project dependencies.

Namely:

1. Air
2. Dagger
3. Golangci-lint
4. Licensei (NOTE: Was already added to nix.)
5. Benthos

• Connected Licensei to the CI.
• Added license-header to all go files.
• Fixed all license-check errors.
• Updated the readme.

Fixes #22

Notes for reviewer

• I haven't been able to find a license for: github.com/couchbase/goprotostellar.

Checklist

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes