Cloning Private Chart Repositories

[stevenpall]

Currently if charts are stored in a private repo (even it's the same repository the action is being run against), the clone will fail. Some possible solutions I've thought of:

• Skip trying to clone the chart repo if it is the same as the target repo; simply use the local path.
• Use ${{ secrets.GITHUB_TOKEN }}. I'm not exactly sure how this would work with raw Git commands. I believe this also requires the use of https://, so chart git URLs would need to be altered from the ssh://git@github.com format Flux uses.
• Add the ability to pass in an SSH private key so that the script operates in the same way as Flux.

Thoughts?

[stefanprodan]

Adding an optional isLocal or similar flag could be an option.

[stevenpall]

@stefanprodan I took a stab at the personal access token approach in #15. I think this is the better solution as it covers situations where charts are stored in the same repo as releases as well as ones where charts are stored in a separate (private) repo.