feat(acme): support EAB credentials

Co-authored-by: techknowlogick <164197+techknowlogick@users.noreply.github.com>

custom/conf/app.example.ini

@@ -264,6 +264,11 @@
 ;; ACME profile to request from the CA (e.g. "shortlived" for raw-IP certificates)
 ;ACME_PROFILE =
 ;;
+;; External account binding credentials; set both to enable EAB
+;; ACME_EAB_HMAC should be a base64url-encoded MAC key
+;ACME_EAB_KID =
+;ACME_EAB_HMAC =
+;;
 ;; ACME live directory (not to be confused with ACME directory URL: ACME_URL)
 ;; (Refer to caddy's ACME manager https://github.com/caddyserver/certmagic)
 ;ACME_DIRECTORY = https