feat: finish the homepage plugin, move service links and canvas out of core (B19)

drizzle/mysql/0048_hard_demogoblin.sql

@@ -0,0 +1,6 @@
+-- dashboard_service_links, homepage_items and homepage_layouts moved to the
+-- homepage plugin, which adopts them by rename at activation (see
+-- plugins/homepage/migrations/mysql/0001_adopt_homepage_tables.sql).
+-- Dropping them here would delete every row before the plugin's migration
+-- ever runs, since this runs at boot before the plugins table exists.
+SELECT 1;