Add versioning to docs

[masci]

Please check if the PR fulfills these requirements

• The PR has no duplicates (please search among the Pull Requests before creating one)
• The PR follows our contributing guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

• What kind of change does this PR introduce?

This PR introduces Mike to wrap Mkdocs execution so that we can build different docs for each different Arduino CLI version.

• What is the current behavior?

At the moment docs are built and published at every merge on master, meaning that the docs might contain unreleased features.

• What is the new behavior?

We'll add:

• a special latest version of the docs pointing to the most recent Arduino CLI release: these docs will be shown by default when landing to https://arduino.github.io/arduino-cli/

• a special dev version of the docs, documenting whatever we have on master at every commit

• a selector to pick the right version of the docs for the Arduino CLI version users have installed

• Does this PR introduce a breaking change?

No, existing docs will be preserved, new ones will follow the versioning strategy.

• Other information:

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See how to contribute

[rsora]

An unwanted blank line maybe?

[rsora]

Excellent!