Document how to provide credentials for private Git repos

[OneCricketeer]

What is your environment, configuration, and command?

Latest version as of this issue - idpbuilder 0.7.0 go1.21.3 darwin/amd64

Running idpbuilder create -p https://github.com/cnoe-io/<a private repo>//ref-implementation

What did you do and What did you see instead?

Services started, but it was unable to clone them into Gitea showing repeated errors of cloning repo: authentication required

Additional Information. Logs.

Please create documentation on how to handle creation with private stacks.

[OneCricketeer]

Probably related to #237

[nabuskey]

https://cloud-native.slack.com/archives/C05TN9WFN5S/p1724892781490279?thread_ts=1724877726.695989&cid=C05TN9WFN5S

I helped Abby with this. Please see if this works for you.
I will have to document this part as well.

[OneCricketeer]

@nabuskey This thread seems to be about Gitea, when I want to use a private repo from Github with the --packages arg.

The current workaround is to clone locally, then provide a local folder as the package

[nabuskey]

We have a draft PR for supporting private repositories with SSH (private key). #405

Also documented here: https://cnoe.io/docs/reference-implementation/installations/idpbuilder/usage#example-commands

We need to decide what we want to do in the PR.