Support polling git repositories for new branches/revisions

This is mostly a workaround for the occasional problems with the guix-commits
mailing list, as it can break and then the data service doesn't learn about
new revisions until the problem is fixed.

I think it's still a generally good feature though, and allows deploying the
data service without it consuming emails to learn about new revisions, and is
a step towards integrating some kind of way of notifying the data service to
poll.

sqitch/deploy/git_repositories_poll_interval.sql

@@ -0,0 +1,8 @@
+-- Deploy guix-data-service:git_repositories_poll_interval to pg
+
+BEGIN;
+
+ALTER TABLE git_repositories
+  ADD COLUMN poll_interval INTEGER DEFAULT NULL;
+
+COMMIT;

sqitch/revert/git_repositories_poll_interval.sql

@@ -0,0 +1,7 @@
+-- Revert guix-data-service:git_repositories_poll_interval from pg
+
+BEGIN;
+
+-- XXX Add DDLs here.
+
+COMMIT;

sqitch/sqitch.plan

@@ -96,3 +96,4 @@ blocked_builds_blocked_builds_blocked_derivation_output_details_set_id_2 2023-03
 guix_revision_package_derivation_distribution_counts 2023-03-08T16:53:44Z Chris <chris@felis> # Add guix_revision_package_derivation_distribution_counts table
 cascade_nar_foreign_keys 2023-08-01T09:42:33Z Chris <chris@felis> # Make it easier to delete nars entries
 nar_indexes 2023-08-01T11:37:35Z Chris <chris@felis> # Add nar related indexes
+git_repositories_poll_interval 2023-10-08T20:36:09Z Chris <chris@felis> # Add git_repositories.poll_interval

sqitch/verify/git_repositories_poll_interval.sql

@@ -0,0 +1,7 @@
+-- Verify guix-data-service:git_repositories_poll_interval on pg
+
+BEGIN;
+
+-- XXX Add verifications here.
+
+ROLLBACK;