Add explicit auth for allowing backup

[russorat]

we need to add an additional authorization that can be added to a token that allows the user to run a backup.

We will also need to migrate all master tokens to have this authorization.

[kelwang]

related to #16120

[lesam]

2.0 backups currently require the root token, per the docs: https://docs.influxdata.com/influxdb/v2.0/backup-restore/backup/

Is the intention still to have this requirement?

[lesam]

i.e. the point of this issue is that instead of the root token, we should also allow a token with a new 'backup' permission to perform backup and/or restore?

[lesam]

I believe this is a dup of #21092 - @russorat can we close this one?