[V2] - Add Tag system for requests

[konradlang]

Verification required - issue still open in V2:

add a simple tagging system for requests, so that the Negotiator admin (initially) or network admin (later) can add tags to the requests and we can filter based on those

controlled vocabularly - just M:N mapping to requests to tags

initially we can propose some but later people can easily do their own tag proposals

(so basically a tag listing table and then table with mapping tags to requests)