fix: switch to datadog v2 gem (#12214)

# Pull Request Template

## Description
- The `0.48` version of the `ddtrace` gem was out of date, which was
causing the application to crash if `DD_AGENT_URL` was configured
- Switch to `datadog` gem, which is the currently maintained gem from DD


Ref: https://github.com/DataDog/dd-trace-rb/releases/tag/v2.0.0

Gemfile

@@ -108,7 +108,7 @@ gem 'google-cloud-translate-v3', '>= 0.7.0'
 ##-- apm and error monitoring ---#
 # loaded only when environment variables are set.
 # ref application.rb
-gem 'ddtrace', require: false
+gem 'datadog', '~> 2.0', require: false
 gem 'elastic-apm', require: false
 gem 'newrelic_rpm', require: false
 gem 'newrelic-sidekiq-metrics', '>= 1.6.2', require: false