Update telemetry support

[AndrewFerr]

• add config to specify a custom telemetry room to join/create
• render Matrix events in a human-readable format
• support basic auth for HTTP endpoint
• use shared IDs for telemetry event & room types
• refactor for parity with with Synapse telemetry

[AndrewFerr]

I've done some local ad-hoc testing on this, and believe it can be ready to go.

[AndrewFerr]

Also pinging @buffless-matt for feedback, as this PR is largely based on the Synapse telemetry module.

[buffless-matt]

@AndrewFerr I just scanned the diff for feature parity with the Synapse telemetry module, leaving the code review for Tadzik.