New CLI doesn't support automatic detection of Git providers

[alexott]

Right now the Git provider name is a required argument, while old CLI was able to deduce "well-known" Git providers automatically, based on the Repo URL: https://github.com/databricks/databricks-cli/blob/main/databricks_cli/sdk/service.py#L1582 - it was very convenient.

[pietern]

@alexott Please take a look at the linked PR; it should do the trick.

[alexott]

We also don't print allowed provider values in the help.