Create Tag Count Aggregation

[zicklag]

https://zicklag.katharos.group/blog/how-to-federate/#aggregation

For aggregation we will start by doing it on the Weird.One instance, and instances can either also do the aggregation themselves, or trust Weird.one to do it.

We need to:

• Create job that will count the users in each tag, from the global tag index.
• Update a global mapping that contains the tag counts.
• Anybody can write to this global mapping, it's up to the instance which author they trust.