Expand Datadog instrumentation (#12908)

Expand Datadog instrumentation

This commit adds extra telemetry in Datadog for:

- Redis
  - We make 3 different Redis connections available, so this change
    shows us _which_ Redis instance a given query goes to
- Split HTTP requests by domain using:
  - net/http - default for Ruby
  - faraday - used by:
    - buffer
    - elasticsearch
    - gibbon
    - oauth2
    - octokit
    - sawyer
    - twilio
  - excon - used by:
    - fog
- AWS
- RestClient
  - Cloudinary
  - Pusher
- concurrent-ruby
  - ActiveSupport
  - brpoplpush-redis_script
  - i18n
  - sidekiq-unique-jobs
  - sprockets (do we even use this?)
- httpclient
  - pusher
- http.rb
  - twitter (omniauth)
  - honeycomb

app/lib/forem_stats_drivers/datadog_driver.rb

@@ -9,9 +9,18 @@ module ForemStatsDrivers
         c.tracer priority_sampling: true
         c.use :elasticsearch
         c.use :sidekiq
-        c.use :redis
+        c.use :redis, service_name: "redis", describes: { url: ENV["REDIS_URL"] }
+        c.use :redis, service_name: "redis-sessions", describes: { url: ENV["REDIS_SESSIONS_URL"] }
+        c.use :redis, service_name: "redis-sidekiq", describes: { url: ENV["REDIS_SIDEKIQ_URL"] }
         c.use :rails
-        c.use :http
+        c.use :http, split_by_domain: true
+        c.use :faraday, split_by_domain: true
+        c.use :excon, split_by_domain: true
+        c.use :httpclient, split_by_domain: true
+        c.use :httprb, split_by_domain: true
+        c.use :aws
+        c.use :rest_client
+        c.use :concurrent_ruby
       end
       Datadog::Statsd.new
     end