Feat: create `meta.json` on checkoutg

[mwilck]

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

If a local repository is checked out after osc fork; osc co, it contains meta data taht allows e.g. osc build to run. This meta data is stored in the parent (project) directory under .osc/_project and .osc/_apiurl. This meta data is only valid for the checked-out branch in the git repo (from scmsync). If the repo directory is copied or moved somewhere else, the meta data is lost.

Describe the solution you'd like

When osc co checks out a project that is using scmsync for source code management,
fill in .git/obs/meta.json automatically for the checked-out branch.

It would be even nicer to fill in this data for all branches in the git clone, but I guess that's impossible because this data is not stored in gitea but in OBS.

@dmach: as discussed on Slack.