Add Description to Tags (for Tag Management)

Current Situation: Tags have no additional metadata visible

Current Problem(s):

• There's no in-built way to explain what a tag means - you need to e.g. use an external spreadsheet then remember to do that and periodically reconcile
• As a result, it's difficult esp for staff who did not create the tag, to know what it is for precisely.
• This gets worse the more tags there are and the older the account is

This dovetails with other feature requests about being to see both contacts and assets that use said tags from the Tag interface itself, although the former you can do with contact groups easily enough, the latter is close to impossible.

Desired Situation:

* At minimum, add a "Description" field that is editable

* Could also introduce Categories to help manage these better

* It would be helpful to have a count of and links to where the tag is used across the system

* As well as the last time the tag was used - either to write or read in an automation