[minor] Automate Traefik certificate rotation

[joecorall]

Add an idempotent Let's Encrypt hook with certificate validation, Traefik-only recreation, health verification, and Slack failure alerts.

Tested on as-test.lib.lehigh.edu

$ ssh as-test.lib.lehigh.edu
$ cd /opt/archivesspace
$ sudo install -o root -g root -m 0600 \
  scripts/local-cert-hook.env.example \
  /etc/default/local-cert-hook
$ sudo vim.tiny /etc/default/local-cert-hook # added slack webhook that posts to `#libtech-deployments`
$ sudo install -o root -g root -m 0755 \
   scripts/lehigh-certs.sh \
   /usr/local/sbin/local-cert-hook
$ make lehigh-certs
[+] up 1/1
 ✔ Container traefik Healthy                                                                                                                                                     8.7s
TLS certificate copied; Traefik is healthy.

Related Discussion

https://lehigh-lts.slack.com/archives/C0568N85KMF/p1784314841304189

LetsEncrypt will renew the cert on September 20 at 6:47am .. We probably should hold off merging this PR until then.