firefly-iii: Connect to external PostgreSQL

Since the new database server outside the Kubernetes cluster, created
for Authelia, was seeded from a backup of the in-cluster server, it
already contained the data from Firefly-III as well.  Thus, we can
switch Firefly-III to using it, too.

The documentation for Firefly-III does not mention anything about how
to configure it to use certificate-based authentication for PostgreSQL,
as is required by the new server.  Fortunately, it ultimately uses
_libpq_, so the standard `PG...` environment variables work fine.  We
just need a certificate issued by the _postgresql-ca_ ClusterIssuer and
the _DCH Root CA_ certificate mounted in the Firefly-III container.

firefly-iii/firefly-iii.env

@@ -7,10 +7,13 @@ TZ=America/Chicago
 TRUSTED_PROXIES=172.30.0.160/28
 
 DB_CONNECTION=pgsql
-DB_HOST=default.postgresql
+DB_HOST=postgresql.pyrocufflink.blue
 DB_PORT=5432
-DB_USERNAME=firefly-iii.firefly
+DB_USERNAME=firefly
 DB_DATABASE=firefly
+PGSSLROOTCERT=/run/dch-ca/dch-root-ca.crt
+PGSSLCERT=/run/secrets/firefly/postgresql/tls.crt
+PGSSLKEY=/run/secrets/firefly/postgresql/tls.key
 
 CACHE_DRIVER=redis
 SESSION_DRIVER=redis