caddy: bump up caddy to 2.7.3 (#936)

This commit bumps up Caddy and mitigates all the high and critically
reported findings.

Author: evict

docker-compose/docker-compose.yaml

@@ -69,7 +69,7 @@ services:
   # https://caddyserver.com/docs/caddyfile
   caddy:
     container_name: caddy
-    image: 'index.docker.io/caddy:2.5.2-alpine@sha256:cfa7d94aa1f0c68a167b147a8573711283df2cd6fc285d220387f20206ff4874'
+    image: 'index.docker.io/caddy:2.7.3-alpine@sha256:f9824933254e3e43e0508670ee9bdcde704621017e95119a05317383b1878f4f'
     cpus: 4
     mem_limit: '4g'
     environment: