metrics of bridges per distributor and assignments

As part of bridgedb#40031 (closed) bridgedb is not having anymore the complete information of distributors and bridges. rdsys is the one having the full picture of assignments and bridgedb only sees the bridges that are assigned to it.

That means that bridgedb will not be able anymore to produce the bridgedb-pool-assignments and we should produce it from rdsys. Also the bridgedb-metrics internal.*.byipv*-bysubring* metrics will only include the distrubtors run by bridge (moat, email and https) and not the new ones (moat settings or telegram), but I guess this is a bit less important.