Add a new table guix_revision_lint_checkers

To associate a set of lint checkers with a specific revision. While there is
the association through the lint warnings, that only works for checkers where
there are lint warnings for that revision.

Therefore, to allow finding all the checkers for a specific revision, also
associate them directly with the revision.

sqitch/deploy/guix_revision_lint_checkers.sql

@@ -0,0 +1,11 @@
+-- Deploy guix-data-service:guix_revision_lint_checkers to pg
+
+BEGIN;
+
+CREATE TABLE guix_revision_lint_checkers (
+  lint_checker_id integer NOT NULL REFERENCES lint_checkers (id),
+  guix_revision_id integer NOT NULL REFERENCES guix_revisions (id),
+  PRIMARY KEY (lint_checker_id, guix_revision_id)
+);
+
+COMMIT;