Create `saml_group_links` database table

Creates a table to store SAML Group Links, similar to LDAP
Group Links.

db/migrate/20201012194936_create_saml_group_links.rb

+# frozen_string_literal: true
+
+class CreateSamlGroupLinks < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    unless table_exists?(:saml_group_links)
+      with_lock_retries do
+        create_table :saml_group_links do |t|
+          t.references :group, foreign_key: { to_table: :namespaces, on_delete: :cascade }, null: false
+          t.timestamps_with_timezone
+          t.integer :access_level, null: false
+          t.text :group_name, null: false
+
+          t.index [:group_id, :group_name], unique: true
+        end
+      end
+    end
+
+    add_text_limit :saml_group_links, :group_name, 255
+  end
+
+  def down
+    with_lock_retries do
+      drop_table :saml_group_links
+    end
+  end
+end

db/schema_migrations/20201012194936

+823d23d8ce8959762a7cadb883ed6d36a46fedaf238ea955d93136277d55cad5
\ No newline at end of file

db/structure.sql

@@ -15752,6 +15752,25 @@ CREATE SEQUENCE routes_id_seq
 
 ALTER SEQUENCE routes_id_seq OWNED BY routes.id;
 
+CREATE TABLE saml_group_links (
+    id bigint NOT NULL,
+    group_id bigint NOT NULL,
+    created_at timestamp with time zone NOT NULL,
+    updated_at timestamp with time zone NOT NULL,
+    access_level integer NOT NULL,
+    group_name text NOT NULL,
+    CONSTRAINT check_1a5ae2ac07 CHECK ((char_length(group_name) <= 255))
+);
+
+CREATE SEQUENCE saml_group_links_id_seq
+    START WITH 1
+    INCREMENT BY 1
+    NO MINVALUE
+    NO MAXVALUE
+    CACHE 1;
+
+ALTER SEQUENCE saml_group_links_id_seq OWNED BY saml_group_links.id;
+
 CREATE TABLE saml_providers (
     id integer NOT NULL,
     group_id integer NOT NULL,
@@ -17898,6 +17917,8 @@ ALTER TABLE ONLY reviews ALTER COLUMN id SET DEFAULT nextval('reviews_id_seq'::r
 
 ALTER TABLE ONLY routes ALTER COLUMN id SET DEFAULT nextval('routes_id_seq'::regclass);
 
+ALTER TABLE ONLY saml_group_links ALTER COLUMN id SET DEFAULT nextval('saml_group_links_id_seq'::regclass);
+
 ALTER TABLE ONLY saml_providers ALTER COLUMN id SET DEFAULT nextval('saml_providers_id_seq'::regclass);
 
 ALTER TABLE ONLY scim_identities ALTER COLUMN id SET DEFAULT nextval('scim_identities_id_seq'::regclass);
@@ -19206,6 +19227,9 @@ ALTER TABLE ONLY reviews
 ALTER TABLE ONLY routes
     ADD CONSTRAINT routes_pkey PRIMARY KEY (id);
 
+ALTER TABLE ONLY saml_group_links
+    ADD CONSTRAINT saml_group_links_pkey PRIMARY KEY (id);
+
 ALTER TABLE ONLY saml_providers
     ADD CONSTRAINT saml_providers_pkey PRIMARY KEY (id);
 
@@ -21454,6 +21478,10 @@ CREATE INDEX index_routes_on_path_trigram ON routes USING gin (path gin_trgm_ops
 
 CREATE UNIQUE INDEX index_routes_on_source_type_and_source_id ON routes USING btree (source_type, source_id);
 
+CREATE INDEX index_saml_group_links_on_group_id ON saml_group_links USING btree (group_id);
+
+CREATE UNIQUE INDEX index_saml_group_links_on_group_id_and_group_name ON saml_group_links USING btree (group_id, group_name);
+
 CREATE INDEX index_saml_providers_on_group_id ON saml_providers USING btree (group_id);
 
 CREATE INDEX index_scim_identities_on_group_id ON scim_identities USING btree (group_id);
@@ -23025,6 +23053,9 @@ ALTER TABLE ONLY clusters_applications_runners
 ALTER TABLE ONLY service_desk_settings
     ADD CONSTRAINT fk_rails_223a296a85 FOREIGN KEY (project_id) REFERENCES projects(id) ON DELETE CASCADE;
 
+ALTER TABLE ONLY saml_group_links
+    ADD CONSTRAINT fk_rails_22e312c530 FOREIGN KEY (group_id) REFERENCES namespaces(id) ON DELETE CASCADE;
+
 ALTER TABLE ONLY group_custom_attributes
     ADD CONSTRAINT fk_rails_246e0db83a FOREIGN KEY (group_id) REFERENCES namespaces(id) ON DELETE CASCADE;