Store cluster metadata in git repository

Feature Request

Is your feature request related to a problem? Please describe:

When maintaining a cluster, it might be possible to lose some important configuration history or other information if a user accidentally removes files or the tiup management node becomes unavailable.

Describe the feature you'd like:

tiup should store cluster topology metadata and access credentials in a git repository. Each cluster should have its own git repository. If a remote is set for the git repository, tiup could push to the remote for each change made to the cluster.

Why the featue is needed:

Describe alternatives you've considered:

It's possible to implement something similar to this by initializing a git repository for the ~/.tiup/storage/cluster/clusters// directory and creating a systemd path unit to monitor that directory for changes.

Teachability, Documentation, Adoption, Migration Strategy:

Start by tracing how tiup uses ~/.tiup/storage/cluster/clusters// for cluster state and metadata. Define how each cluster gets its own Git repository, how topology and access credentials are committed, and when a configured remote receives pushes. Done means the behavior and migration strategy are specified for cluster changes and unavailable management nodes.