Add suggest_pipeline_enabled to application_settings

Adds a setting (default: enabled) to toggle the Suggest Pipeline feature.

Changelog: changed

db/migrate/20210921032008_add_suggest_pipeline_enabled_to_application_settings.rb

+# frozen_string_literal: true
+
+class AddSuggestPipelineEnabledToApplicationSettings < Gitlab::Database::Migration[1.0]
+  def change
+    add_column :application_settings, :suggest_pipeline_enabled, :boolean, default: true, null: false
+  end
+end

db/schema_migrations/20210921032008

+262127539fc16715a56e2cf7426f0f8d24922e26847a01a0a15552d71cd148f8
\ No newline at end of file

db/structure.sql

@@ -10347,6 +10347,7 @@ CREATE TABLE application_settings (
     sidekiq_job_limiter_mode smallint DEFAULT 1 NOT NULL,
     sidekiq_job_limiter_compression_threshold_bytes integer DEFAULT 100000 NOT NULL,
     sidekiq_job_limiter_limit_bytes integer DEFAULT 0 NOT NULL,
+    suggest_pipeline_enabled boolean DEFAULT true NOT NULL,
     CONSTRAINT app_settings_container_reg_cleanup_tags_max_list_size_positive CHECK ((container_registry_cleanup_tags_service_max_list_size >= 0)),
     CONSTRAINT app_settings_ext_pipeline_validation_service_url_text_limit CHECK ((char_length(external_pipeline_validation_service_url) <= 255)),
     CONSTRAINT app_settings_registry_exp_policies_worker_capacity_positive CHECK ((container_registry_expiration_policies_worker_capacity >= 0)),