🐛 create command always checks GitHub for last release, even when OCI is wanted

[jschoone]

/kind bug

What steps did you take and what happened:
[A clear and concise description of what the bug is.]

git clone https://github.com/SovereignCloudStack/cluster-stacks
git clone https://github.com/SovereignCloudStack/csctl
cd csctl
make build
./csctl create ../cluster-stacks/providers/openstack/scs

Got error Error: failed to create create options: failed to create new github client: failed to create git config: environment variable GIT_PROVIDER is not set which is correct in general, but I only want to use an OCI registry

What did you expect to happen:
When no GIT_* env vars are set, the csctl tool could check if there are OCI_* env vars available instead to check for the latest stable version there.
Alternatively or additionally and maybe even more stable could be a flag to set the target, since both GIT_* and OCI_* could be set.

Anything else you would like to add:
[Miscellaneous information that will assist in solving the issue.]

Environment:

• csctl version: (use csctl version)
• OS (e.g. from /etc/os-release):