Add assignments PostgreSQL schema

server/db/schema/assignments.sql

@@ -0,0 +1,16 @@
+CREATE TABLE IF NOT EXISTS public.assignments
+(
+    id integer NOT NULL GENERATED ALWAYS AS IDENTITY ( INCREMENT 1 START 1 MINVALUE 1 MAXVALUE 2147483647 CACHE 1 ),
+    event_id integer NOT NULL,
+    client_id integer NOT NULL,
+    role client_role NOT NULL,
+    CONSTRAINT assignment_pkey PRIMARY KEY (id),
+    CONSTRAINT client_id FOREIGN KEY (client_id)
+        REFERENCES public.clients (id) MATCH SIMPLE
+        ON UPDATE NO ACTION
+        ON DELETE NO ACTION,
+    CONSTRAINT event_id FOREIGN KEY (event_id)
+        REFERENCES public.events (id) MATCH SIMPLE
+        ON UPDATE NO ACTION
+        ON DELETE NO ACTION
+)