feat: add optional topology filter

[achingbrain]

Adds a filter option to topologies to allow filtering out duplicate notifications.

Change checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation if necessary (this includes comments as well)
• I have added tests that prove my fix is effective or that my feature works

[maschad]

Looks good, should we add tests for TopologyFilter ?

[achingbrain]

The registrar test suite has new should use a filter... tests that exercise the code paths, using a PeerFilter which has type overlap with TopologyFilter so I think we're good there.