Merge #1319

1319: Upgrading to a 2048-bit DKIM key r=mergify[bot] a=radtkedev

## What type of PR?

Enhancement

## What does this PR do?

Upgrades to a 2048-bit DKIM key from the currently used and outdated 1024-bit DKIM key.

### Related issue(s)
- #1301 

Co-authored-by: Tom Radtke <tom@radtke.dev>

core/admin/mailu/dkim.py

@@ -5,7 +5,7 @@ They are thus represented as ASCII armored PEM.
 from OpenSSL import crypto
 
 
-def gen_key(key_type=crypto.TYPE_RSA, bits=1024):
+def gen_key(key_type=crypto.TYPE_RSA, bits=2048):
     """ Generate and return a new RSA key.
     """
     key = crypto.PKey()