[v2.9] Add "registryconfig-auth-" secrets to backup rules

[mallardduck]

This PR helps address the issue here: https://github.com/rancher/rancher/issues/44033

The fix being done here versus where the original issue planned means we can deliver a partial fix rather easily here. And a more complete fix that could take more time can still be done later.

This fix relies on a different BRO resourceset rule than they planned on using. And our fix will only catch secrets made via Rancher with the default generated name prefix registryconfig-auth- but not any secrets that the user creates outside of the "Cluster Creation UI" that may have different names.

As this is a chart change it needs to be:

• Merged here,
• Tagged in a release here, and
• New rancher/charts release to match.

It should also be back ported to 2.8 at the very least. Unlikely worth the effort to do that for 2.7 too.