docs: add versioning with mike

[michalsn]

Description
This PR adds docs versioning using mike, published to the gh-pages branch.

Deploy rules

• Push to develop: deploys the dev docs (work-in-progress)
• Push a vX.Y.Z tag (e.g. v1.1.0): deploys docs under <major>.<minor> (e.g. 1.1), updates the latest alias, and sets it as the default version (site root redirects here)
• Pre-release tags (e.g. v1.1.0-rc1): are skipped

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[michalsn]

Thanks @paulbalandan If you have time, please take a look at this as well: codeigniter4/settings#166