Extend git secret creation to include CA

Feature Request

Why

For installations of bigbang such as airgapped installs, it would be beneficial for the git.credentials value to include a caFile attribute for the ability to create a secret that allows flux to trust self-signed certificates for https connections.

Flux gitrepository documentation

Proposed Solution

Adding caFile or similar attribute to the git.credentials values and enabling this value to be added to the git-credentials.yaml template for https authentication.