feat(web/panettone): Add a system for database migrations

Add a system for writing, running, and tracking database
migrations (changes to the database schema) over time, inspired by but
significantly simpler than postmodern-passenger-pigeon.

Migrations can be generated by
running (PANETTONE.MODEL:GENERATE-MIGRATION "name"), and are numerically
ordered lisp files that define (at least) a function called UP, which
runs the migration. The migrations that have been run against the
database are tracked in the `migrations` table, and when the
`(PANETTONE.MODEL:MIGRATE)` function is called (as it is on startup),
all migrations that have not yet been run are run within a transaction.

This includes one migration `1-init-schema.lisp`, which migrates the
database (idempotently) to the current state of the schema.

Change-Id: Id243a47763abea649784b12f25a6d05c2267381c
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11253
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>

web/panettone/src/migrations/1-init-schema.lisp

@@ -0,0 +1,23 @@
+"Initialize the database schema from before migrations were added"
+
+(defun ddl/create-issue-status ()
+  "Issue DDL to create the `issue-status' type, if it doesn't exist"
+  (unless (query (:select (:exists (:select 1
+                                    :from 'pg_type
+                                    :where (:= 'typname "issue_status"))))
+                 :single)
+    (query (sql-compile
+            `(:create-enum issue-status ,panettone.model:+issue-statuses+)))))
+
+(defun ddl/create-tables ()
+  "Issue DDL to create all tables, if they don't already exist."
+  (dolist (table '(panettone.model:issue
+                   panettone.model:issue-comment
+                   panettone.model:issue-event
+                   panettone.model:user-settings))
+    (unless (table-exists-p (dao-table-name table))
+      (create-table table))))
+
+(defun up ()
+  (ddl/create-issue-status)
+  (ddl/create-tables))