Rework the builds and build_status tables as well as related code

Allow for build status information to be submitted by POST request. This
required some changes to the builds and build_status tables, as for example,
the Cuirass build id may not be available, and the derivation may not be know
yet, so just record the derivation file name.

sqitch/deploy/rework_builds.sql

@@ -0,0 +1,21 @@
+-- Deploy guix-data-service:rework_builds to pg
+
+BEGIN;
+
+DROP TABLE build_status;
+DROP TABLE builds;
+
+CREATE TABLE builds (
+    id integer PRIMARY KEY GENERATED ALWAYS AS IDENTITY,
+    build_server_id integer NOT NULL REFERENCES build_servers(id),
+    derivation_file_name varchar NOT NULL
+);
+
+CREATE TABLE build_status (
+    id integer PRIMARY KEY GENERATED ALWAYS AS IDENTITY,
+    build_id integer NOT NULL REFERENCES builds(id),
+    "timestamp" timestamp without time zone DEFAULT clock_timestamp() NOT NULL,
+    status guix_data_service.buildstatus NOT NULL
+);
+
+COMMIT;