Set UMask for metadata and doveauth systemd units to 0700

[link2xt]

It seems when metadata or doveauth get to mkdir user directory in vmail first, they create it with too broad permissions:

total 41M
drwx------ 5 vmail vmail 4.0K Sep 22 00:03 .
drwx------ 1 vmail vmail  40M Nov  7 20:39 ..
drwx------ 2 vmail vmail 4.0K Jul 13 18:22 cur
-rw------- 1 vmail vmail 2.3K Sep 21 08:09 dovecot.index.log
-rw------- 1 vmail vmail  452 Jul 13 18:22 dovecot.list.index.log
-rw------- 1 vmail vmail   51 Jul 13 18:22 dovecot-uidlist
-rw------- 1 vmail vmail    8 Jul 13 18:22 dovecot-uidvalidity
-r--r--r-- 1 vmail vmail    0 Jul 13 18:22 dovecot-uidvalidity.6692a9dc
-rw------- 1 vmail vmail    0 Jul 13 18:22 maildirfolder
-rw-r--r-- 1 vmail vmail  199 Sep 21 08:09 metadata.json
-rw-r--r-- 1 vmail vmail    0 Sep 21 08:09 metadata.json.lock
drwx------ 2 vmail vmail 4.0K Jul 13 18:22 new
-rw-r--r-- 1 vmail vmail  120 Sep 21 02:00 password
drwx------ 2 vmail vmail 4.0K Jul 13 18:22 tmp

In this case above the folder is 0700, but some folders are 755 because of this. We should make sure all created folders are 755.

It's not a security issue as long as /home/vmail/mail is 0700, but still not nice that different user folders have different permissions based on timing.