Add new observability feature and policy

...ews/projects/settings/operations/_observability.html.haml

config/feature_flags/development/observability_metrics.yml

config/feature_flags/wip/observability_features.yml

ee/app/controllers/projects/logs_controller.rb

ee/app/controllers/projects/metrics_controller.rb

ee/app/controllers/projects/tracing_controller.rb

ee/app/models/gitlab_subscriptions/features.rb

ee/app/policies/ee/project_policy.rb

...shared/usage_quotas/tabs_content/_observability.html.haml

ee/lib/ee/sidebars/projects/menus/monitor_menu.rb

ee/spec/lib/ee/sidebars/projects/menus/monitor_menu_spec.rb

ee/spec/policies/project_policy_spec.rb

ee/spec/requests/projects/logs_controller_spec.rb

ee/spec/requests/projects/metrics_controller_spec.rb

ee/spec/requests/projects/tracing_controller_spec.rb

lib/gitlab/observability.rb

spec/lib/gitlab/auth_spec.rb

spec/lib/gitlab/observability_spec.rb