feat: add required trunk version, and update version check

[ctron]

This PR makes trunk aware of its version. Enabling two features with that:

1. Allow enforcing a trunk version for a project. This allows one to require a certain trunk version for a project, e.g. in the case user newer features from trunk.
2. Implement an "update check", so that trunk can let you know that there's a newer version available.

The update check can be disabled by disabling the feature update_check. This might be useful for packagers, like nix and homebrew.