Rework kopia manifest tagging in corso

[ashmrtn]

The tags for kopia manifests that we use right now is rather scattershot. We have tags on item data snapshots but not really much else. This makes it difficult to do things like garbage collect failed backups, filter backups by type, protected resource, or otherwise

Some things that should be cleaned up/changed:

• Tag backup models with reasons #3976
• tag backups and models with tenant ID
• clearer tag keys for protected resource ID, tenant ID, and reason (i.e. should be clear which is which given a set of tags)
• tag kopia checkpoints so we can exclude and/or garbage collect them explicitly