[RFE] Update UI to allow choosing a ResourceSet on Backup creation

[jbiers]

SURE-9545

Describe the solution you'd like
When creating a Backup resource using the Backup&Restore Operator, a user goes to the following screen:

We want to add a new section to this screen, called ResourceSets. It will be meant for setting the value of the spec.resourceSetName. field in the Backup CR.

Ideally, this section will contain a dropdown menu with all ResourceSet resources available in the cluster, and will currently default to rancher-resource-set.

Along with the dropdown, a line of text with the content "Enabling encryption is highly recommended when using rancher-resource-set-full, otherwise sensitive information will be backed up as plain-text. Read more." should be added. Note that "read more" is a link to the relevant docs page and section.

Additional context
rancher/backup-restore-operator#607

[richard-cox]

@jbiers Will there be any RBAC issues with ResourceSet, how many ResourceSet's would you imagine customers have (10s, 1000s, 10,000s)?

Note for anyone working on this, ResourceSet is resources.cattle.io.resourceset visible once Rancher Backups is installed on upstream/local cluster. The screen in question is Rancher Backups --> Backup --> Create. The name of the section should just be Resource Set

[jbiers]

@richard-cox I don't think any RBAC issues will be faced. As for number of resources, I'd expect users to have no more than a couple 10s.