Invoke with `bricks sync SRC DST`.
In bundle context `SRC` and `DST` arguments are taken from bundle configuration.
This PR adds `bricks bundle sync` to disambiguate between the two.
Once the VS Code extension is bundle aware they can again be consolidated.
Consolidating them today would regress the VS Code experience if a
`bundle.yml` file is present in the file tree.
By:
* Add .gitkeep to retain test fixture directories under
./python/testdata
* Move GitHub related functionality to ./experimental (it is not in use)
* Comment out test in ./cmd/sync
* Fix test in ./git
Pieter Noordhuis
shreyas-goenka
Serge Smertin