Add support of pki for custom repositories

[DriverXavGeForce]

Custom repositories access can be restricted using pki.
Adding support of pki with additional parameters in the command rmt-cli repos custom add should help to manage this type of custom repositories.
Example:
rmt-cli repos custom add --ca-cert=mycacert.pem --certificate=mycert.pem --private-key=mykey.key https://my_repo_url my_repo_name