Add cache tracing and Redis tracing

This change adds Distributed Tracing support for two new types of events

1. Redis Calls
1. ActiveSupport (Rails) Caching Operations

The intention is to help application developers and infrastructure
SREs to understand the pressure that caching operations can have on
the application when running at scale.

The Redis and Caching spans can be viewed in the Jaeger UI by clicking
the "Trace" link in the performance bar when running on GDK.

Gemfile

@@ -295,7 +295,7 @@ gem 'sentry-raven', '~> 2.9'
 gem 'premailer-rails', '~> 1.9.7'
 
 # LabKit: Tracing and Correlation
-gem 'gitlab-labkit', '~> 0.4.2'
+gem 'gitlab-labkit', '~> 0.5'
 
 # I18n
 gem 'ruby_parser', '~> 3.8', require: false

Gemfile.lock

@@ -335,12 +335,13 @@ GEM
     gitaly (1.58.0)
       grpc (~> 1.0)
     github-markup (1.7.0)
-    gitlab-labkit (0.4.2)
+    gitlab-labkit (0.5.2)
       actionpack (~> 5)
       activesupport (~> 5)
       grpc (~> 1.19)
       jaeger-client (~> 0.10)
       opentracing (~> 0.4)
+      redis (> 3.0.0, < 5.0.0)
     gitlab-license (1.0.0)
     gitlab-markup (1.7.0)
     gitlab-sidekiq-fetcher (0.5.1)
@@ -742,7 +743,7 @@ GEM
     rails-dom-testing (2.0.3)
       activesupport (>= 4.2.0)
       nokogiri (>= 1.6)
-    rails-html-sanitizer (1.0.4)
+    rails-html-sanitizer (1.2.0)
       loofah (~> 2.2, >= 2.2.2)
     rails-i18n (5.1.1)
       i18n (>= 0.7, < 2)
@@ -1135,7 +1136,7 @@ DEPENDENCIES
   gettext_i18n_rails_js (~> 1.3)
   gitaly (~> 1.58.0)
   github-markup (~> 1.7.0)
-  gitlab-labkit (~> 0.4.2)
+  gitlab-labkit (~> 0.5)
   gitlab-license (~> 1.0)
   gitlab-markup (~> 1.7.0)
   gitlab-sidekiq-fetcher (= 0.5.1)

changelogs/unreleased/labkit-cache-tracing.yml

+---
+title: Add Redis interceptor tracing
+merge_request: 30238
+author:
+type: other

config/initializers/tracing.rb

@@ -21,9 +21,13 @@ if Labkit::Tracing.enabled?
     end
   end
 
+  # Instrument Redis
+  Labkit::Tracing::Redis.instrument
+
   # Instrument Rails
   Labkit::Tracing::Rails::ActiveRecordSubscriber.instrument
   Labkit::Tracing::Rails::ActionViewSubscriber.instrument
+  Labkit::Tracing::Rails::ActiveSupportSubscriber.instrument
 
   # In multi-processed clustered architectures (puma, unicorn) don't
   # start tracing until the worker processes are spawned. This works