Change subcommand velero restic to velero repo

[allenxu404]

Signed-off-by: allenxu404 qix2@vmware.com

Thank you for contributing to Velero!

Please add a summary of your change

• Use velero repo get to obtain BackupRepositories instead of using velero restic repo get

Does your change fix a particular issue?

Fixes #5098

Please indicate you've done the following:

• Accepted the DCO. Commits without the DCO will delay acceptance.
• Created a changelog file or added /kind changelog-not-required as a comment on this pull request.
• Updated the corresponding documentation in site/content/docs/main.

[Lyndon-Li]

@danfengliu
Please pay attention to this change, the command velero restic repo get has been changed to velero repo get.
I searched the e2e code and didn't see anywhere invoking the velero restic repo get cli, so this change should not affect e2e.
Please double check this. Thanks.