feat(docs): script to gen godoc and publish on gh-pages

[moul]

• script to fill the docs/ folder with things that can be generated from source (godoc, what else?)
• github actions calling that script, then publishing the content on the gh-pages branch when a PR is merged on master

Once merged, we'll see the result and will be able to make it better, i.e., adding index, custom theme, fix broken links.

Btw, we need this because the current LICENSE file is not supported by pkg.go.dev.

Contributors Checklist

• Added new tests, or not needed, or not feasible
• Provided an example (e.g. screenshot) to aid review or the PR is self-explanatory
• Updated the official documentation or not needed
• No breaking changes were made, or a BREAKING CHANGE: xxx message was included in the description
• Added references to related issues and PRs
• Provided any useful hints for running manual tests

Maintainers Checklist

• Checked that the author followed the guidelines in CONTRIBUTING.md
• Checked the conventional-commit (especially PR title and verb, presence of BREAKING CHANGE: in the body)
• Ensured that this PR is not a significant change or confirmed that the review/consideration process was appropriate for the change

[ajnavarro]

LGTM