📦️(mail): make DIR_MAILS variable changeable

That allows downstream packages to e.g. split the builds of
frontend/backend/mail, as it's the case in nixpkgs:
NixOS/nixpkgs@5597a4f

Signed-off-by: Maximilian Bosch <[email protected]>

Author: Ma27

src/mail/bin/html-to-plain-text

@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
 set -eo pipefail
 # Run html-to-text to convert all html files to text files
-DIR_MAILS="../backend/core/templates/mail/"
+DIR_MAILS="${DIR_MAILS:-../backend/core/templates/mail}/"
 
 if [ ! -d "${DIR_MAILS}" ]; then
   mkdir -p "${DIR_MAILS}";

src/mail/bin/mjml-to-html

@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
 
 # Run mjml command to convert all mjml templates to html files
-DIR_MAILS="../backend/core/templates/mail/html/"
+DIR_MAILS="${DIR_MAILS:-../backend/core/templates/mail}/html/"
 
 if [ ! -d "${DIR_MAILS}" ]; then
   mkdir -p "${DIR_MAILS}";