Merge MultiReporter into Reporter

[tillberg]

This adds additional configuration options to the Reporter. One of the added configuration options includes the ability to specify multiple MeasurementsCommunicators. This obviates the need for the separate MultiReporter.

This also makes a couple minor improvements:

• Removes an old quirk: instead of sending metrics at a random offset from the minute, metrics are now sent at the top of each minute. This is probably what everyone wants and expects.
• Adds a Close function to the Reporter that blocks for up to ~5 seconds while attempting to send a final batch of measurements to each MeasurementsCommunicator.

[lucky]

lol i got a notification for this

[dkuebric]

same 👋