refactor(web/panettone): Use postmodern connection pools

Instead of managing Postgres connections on our own, use the
`with-connection` postmodern function with pooling enabled as a route
decorator.

This should resolve at least some of the issues from b/113 with
leaking connections, and an unreported issue with connections being
reused while transactions are in progress.

Change-Id: I1ed68667a3240900de1ae69df37d2d3018caf204
Reviewed-on: https://cl.tvl.fyi/c/depot/+/5198
Tested-by: BuildkiteCI
Reviewed-by: eta <tvl@eta.st>
Autosubmit: tazjin <tazjin@tvl.su>

web/panettone/src/packages.lisp

@@ -32,7 +32,9 @@
   (:use :cl :panettone.util :klatre :postmodern :iterate)
   (:import-from :alexandria :if-let :when-let :define-constant)
   (:export
-   :connect-postgres :ddl/init :make-thread
+   :prepare-db-connections
+   :ddl/init
+   :*pg-spec*
 
    :user-settings
    :user-dn :enable-email-notifications-p :settings-for-user
@@ -76,7 +78,7 @@
    :panettone.model
    :id :subject :body :author-dn :issue-id :status :created-at
    :field :previous-value :new-value :acting-user-dn
-   :issue-comments :num-comments :issue-events)
+   :*pg-spec*)
   (:import-from :panettone.irc :send-irc-notification)
   (:shadow :next)
   (:export :start-pannetone :config :main))