Allow tagging of multiple save-and-restore snapshots in a single operation

[georgweiss]

User may select multiple snapshots in tree view or search result view in order to apply same tag. This has been possible for golden tags, but is hence now extended to support free text tags as well.

Checklist

• Testing:

  • The feature has automated tests
  • [ X] Tests were run

• Documentation:

  • [ X] The feature is documented
  • [ X] The documentation is up to date
  • Release notes:
    • Added an entry if the change is breaking or significant
    • Added an entry when adding a new feature