Refactor Histogram metrics to be homeserver-scoped

[MadLittleMods]

Bulk refactor Histogram metrics to be homeserver-scoped. We also add lints to make sure that new Histogram metrics don't sneak in without using the server_name label (SERVER_NAME_LABEL).

Part of #18592

Testing strategy

1. Add the metrics listener in your homeserver.yaml

   listeners:
     # This is just showing how to configure metrics either way
     #
     # `http` `metrics` resource
     - port: 9322
       type: http
       bind_addresses: ['127.0.0.1']
       resources:
         - names: [metrics]
           compress: false
     # `metrics` listener
     - port: 9323
       type: metrics
       bind_addresses: ['127.0.0.1']

2. Start the homeserver: poetry run synapse_homeserver --config-path homeserver.yaml
3. Fetch http://localhost:9322/_synapse/metrics and/or http://localhost:9323/metrics
4. Observe response includes the TODO metrics with the server_name label

Todo

• Wait for Refactor Counter metrics to be homeserver-scoped #18656 to merge

Dev notes

LoggingDatabaseConnection
make_conn
make_pool
make_fake_db_pool

Pull Request Checklist

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• Code style is correct (run the linters)

[devonh]

These changes all look pretty straightforward and use the same patterns as the other metrics changes. 👍

...assuming CI passes of course :)

[MadLittleMods]

Thanks for the review @devonh 🦩