feat: OAuth implementation with Discord

This commit separates the core features of GéJDR from the backend as
these will also be used by the bot in the future.

This commit also updates the dependencies of the project. It also
removes the dependency lettre as well as the mailpit docker service
for developers as it appears clearer this project won’t send emails
anytime soon.

The publication of a docker image is also postponed until later.

gejdr-core/migrations/20240809173617_users.down.sql

@@ -0,0 +1,3 @@
+-- Add down migration script here
+DROP TABLE IF EXISTS public.users;
+DROP EXTENSION IF EXISTS "uuid-ossp";

gejdr-core/migrations/20240809173617_users.up.sql

@@ -0,0 +1,15 @@
+-- Add up migration script here
+CREATE EXTENSION IF NOT EXISTS "uuid-ossp";
+
+CREATE TABLE IF NOT EXISTS public.users
+(
+    id character varying(255) NOT NULL,
+    username character varying(255) NOT NULL,
+    email character varying(255),
+    avatar character varying(511),
+    name character varying(255),
+    created_at timestamp with time zone NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    last_updated timestamp with time zone NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    PRIMARY KEY (id),
+    CONSTRAINT users_email_unique UNIQUE (email)
+);