feat(otel): automatic setup based on config

[solnic]

Another follow-up to #886

Automatically configure OpenTelemetry SDK and instrumentation libraries when tracing is enabled, eliminating manual setup boilerplate from user applications.

Before

Users had to manually configure config :opentelemetry and call .setup() on each instrumentation library in Application.start/2:

# application.ex
def start(_type, _args) do
  OpentelemetryBandit.setup()
  Sentry.OpenTelemetry.LiveViewPropagator.setup()
  OpentelemetryPhoenix.setup(adapter: :bandit)
  OpentelemetryOban.setup()
  OpentelemetryEcto.setup([:my_app, :repo], db_statement: :enabled)
  OpentelemetryLoggerMetadata.setup()
  # ...
end

After

All setup is config-driven under integrations: [opentelemetry: [...]]:

config :sentry,
  traces_sample_rate: 1.0,
  integrations: [
    opentelemetry: [
      phoenix: [adapter: :bandit],
      ecto: [repos: [[:my_app, :repo]], db_statement: :enabled]
    ]
  ]

[grantwest]

This is not exclusively a Sentry problem. Not sure the extra complexity is worth it here given that everyone who has telemetry setup is already going to have all of the setup calls in their Application. Additionally all of the Opentelemetry package documentations say to call setup.

Technically a little cleaner, I will certainly grant you that, but maybe going to cause more pain than it is worth.

[solnic]

@grantwest thanks for the input. I believe it is worth the effort and a little bit of extra complexity because it helps with getting started AND hides various implementation details too, actually.

Having said that, this PR will be a proposal, so I welcome all the feedback and we'll figure out if we want to proceed or not 😄