Add initial Docker and Alembic setup

Introduce a `docker-compose.yml` to define the services for backend and database with health checks. Add Alembic configurations for database migrations and an initial empty migration. Include backend-related Docker setup with an entrypoint script for database migration execution.

backend/alembic.ini

@@ -0,0 +1,37 @@
+[alembic]
+script_location = alembic
+sqlalchemy.url = postgresql://postgres:postgres@db:5432/eventspace
+
+[loggers]
+keys = root,sqlalchemy,alembic
+
+[handlers]
+keys = console
+
+[formatters]
+keys = generic
+
+[logger_root]
+level = WARN
+handlers = console
+qualname =
+
+[logger_sqlalchemy]
+level = WARN
+handlers =
+qualname = sqlalchemy.engine
+
+[logger_alembic]
+level = INFO
+handlers =
+qualname = alembic
+
+[handler_console]
+class = StreamHandler
+args = (sys.stderr,)
+level = NOTSET
+formatter = generic
+
+[formatter_generic]
+format = %(levelname)-5.5s [%(name)s] %(message)s
+datefmt = %H:%M:%S