Migrate SearchCounter to internal events

.rubocop_todo/rspec/context_wording.yml

.rubocop_todo/rspec/feature_category.yml

.rubocop_todo/search/namespaced_class.yml

app/controllers/search_controller.rb

config/events/perform_navbar_search.yml

config/events/perform_search.yml

config/metrics/counts_all/20210216180413_all_searches.yml

config/metrics/counts_all/20210216180414_navbar_searches.yml

lib/api/search.rb

lib/gitlab/usage_data_counters.rb

lib/gitlab/usage_data_counters/search_counter.rb

...usage_data_counters/total_counter_redis_key_overrides.yml

spec/controllers/search_controller_spec.rb

...itlab/usage/metrics/instrumentations/redis_metric_spec.rb

spec/lib/gitlab/usage_data_counters/search_counter_spec.rb

spec/requests/api/search_spec.rb

spec/support/rspec_order_todo.yml