Add analytics_sample_rate to all integrations

[delner]

Using the feature defined in #665, and as a follow up to #666, this pull request adds the event sample rate tag, if configured, to the following integrations:

• active_model_serializers
• active_record
• aws
• dalli
• elasticsearch
• excon
• faraday
• grape
• graphql (Add analytics tag to Datadog tracing rmosolgo/graphql-ruby#2154)
• grpc
• http
• mongodb
• mysql2
• rails
• redis
• rest_client
• sequel
• sinatra

[brettlangdon]

We want to use analytics_sample_rate instead of event_sample_rate.

There should be 1 global configuration option analytics when set to true will enable all analytics for all web frameworks only (rack, rails, sinatra, etc)

Each integration will then have it's own 2 configuration options:

• analytics - boolean, whether to explicitly enable or disable for the integration (default: nil so we can test if it was explicitly set or not)
• analytics_sample_rate - float, the sample rate to use for that integration (default: 1.0)

For web frameworks, we should set the tag with analytics_sample_rate if the (global[:analytics] == true && integration[:analytics] != false) or integration[:analytics] == true. Global is true and integration is nil or true or the integration is true.

For everything else, we should set the tag with analytics_sample_rate if integration[:analytics] == true

[delner]

@brettlangdon All of the existing commits have been updated to match the name changes and logic, with the exception of the global flag (which does not yet exist.) I will carry on updating the remaining integrations from here.

[brettlangdon]

these changes look good so far!

[delner]

@brettlangdon Ready for review. Worth pointing out Rails, Sinatra and all the other integrations in this PR are off by default, and will ignore the global flag unless explicitly enabled. Let me know if you'd like to change that behavior.

[brettlangdon]

We probably only want the request spans to have analytics and can remove setting the tag for rendering spans.

Otherwise, this is good to go!

[delner]

@brettlangdon Removed tags from render & cache spans, fixed a constant name, and changed defaults such that only Grape, GraphQL, Rack, Rails, & Sinatra will be toggled by the global flag.

[brettlangdon]

d-(^-^)-b