Merge branch '30392_support_for_multiple_key_value_stores' into 'master'

.flayignore

.gitignore

app/controllers/health_controller.rb

app/models/ci/runner.rb

app/models/project.rb

app/services/metrics_service.rb

app/services/milestones/destroy_service.rb

config/README.md

config/application.rb

config/initializers/7_redis.rb

config/initializers/peek.rb

config/initializers/session_store.rb

config/initializers/sidekiq.rb

config/mail_room.yml

config/redis.cache.yml.example

config/redis.queues.yml.example

config/redis.shared_state.yml.example

...0416_migrate_user_activities_to_users_last_activity_on.rb

doc/administration/high_availability/redis_source.md

doc/administration/operations/cleaning_up_redis_sessions.md