dotty.epfl.ch/docs should provide option to pick up a version that is documented

[romanowski]

Currently dotty.epfl.ch/docs hosts documentation for latest version of the language. This made a lof of sense before 3.0.0 but now, default documentation should indicate that is applicable for stable version and have option to browse documentation and api for current snapshot or older versions.

The most obvious solution may be to host documentation for 3.0.0 (at least one that is marked for 3.0.0) and have an option (dropdown?) to pick latest snapshot or some older version.

We should consider that releases are immutable but documentation is often changed/improved after the release so solution should allow to update the documentation after the release of given version without too much maintenance overhead

[ckipp01]

@romanowski am I assuming correctly that this can be closed now that we do have a dropdown allowing users to go from nightly to stable and vice versa?