Add Phoenix Live Dashboard with Absinthe metrics

[johnshaughnessy]

Experimental

• Upgrade phoenix and other dependencies
• Add phoenix_live_dashboard
• Add request logger
• Add absinthe telemetry events for monitoring graphql api performance

Issues:

• This should be broken into two parts: Upgrade phoenix and other dependencies first, then add phoenix_live_dashboard and absinthe telemetry events.
• Need to make sure elixir/erlang versions running in production are compatible with the upgraded dependencies.

[johnshaughnessy]

If we upgrade cowboy to 2.8, then we need to make sure we are running erlang 22+

See phoenixframework/phoenix#3950

It looks like we are running 22.0 in habitat deploys:
https://github.com/mozilla/hubs-ops/blob/master/plans/erlang/habitat/plan.sh#L3

Need to confirm this and check terraform / hmc

[brianpeiris]

Just noting this here for when we do end up upgrading phoenix. From a discussion in discord:

there is an ugly bug in the toml lib in elixir that causes the server to not start if you update elixir to the latest - fix is easy just bump the toml lib

[johnshaughnessy]

Closing this in favor of #461