feat(artifactapi): add mail stack images to docker registry cache

- ghcr: stalwartlabs/stalwart (Stalwart mail server)
- dockerhub: rspamd/rspamd (spam filter), tozd/postfix (MTA gateway)

apps/base/artifactapi/resources/conf.d/remote-docker.yaml

@@ -9,6 +9,7 @@ remotes:
       - "^kanidm/"
       - "^openvoxproject/"
       - "^stakater/reloader"
+      - "^stalwartlabs/stalwart"
       - "^voxpupuli/puppetboard"
       - "^woodpecker-ci/helm"
     cache:
@@ -35,6 +36,8 @@ remotes:
       - "^hashicorp/vault"
       - "^jfrog/"
       - "^rancher/"
+      - "^rspamd/rspamd"
+      - "^tozd/postfix"
       - "^traefik/"
       - "^ubi9/ubi-minimal"
       - "^victoriametrics/"