feature: improve the output of new/existing dns records

[YouSysAdmin]

Hi.
Slightly improved information output about required DNS changes for new/existing DKIM.

New keys:

‣ NOTE  New DKIM keys have been generated! Please make sure to update your DNS records! You need to add the following details:

**************************************************************
Domain: example1.com
Name: default._domainkey
TYPE: TXT
Value:
"v=DKIM1;h=sha256;k=rsa;s=email;p=****QIDAQAB"

**************************************************************

**************************************************************
Domain: example2.org
Name: default._domainkey
TYPE: TXT
Value:
"v=DKIM1;h=sha256;k=rsa;s=email;p=***EmELQIDAQAB"

**************************************************************

Existing keys:

‣ INFO  Key for domain example1.com already exists in /etc/opendkim/keys/example1.com.private. Will not overwrite.
‣ INFO  Check/Update your DNS records:

**************************************************************
Domain: example1.com
Name: default._domainkey
TYPE: TXT
Value:
"v=DKIM1;h=sha256;k=rsa;s=email;p=***QIDAQAB"

**************************************************************
‣ INFO  Key for domain example2.org already exists in /etc/opendkim/keys/example2.org.private. Will not overwrite.
‣ INFO  Check/Update your DNS records:

**************************************************************
Domain: example2.org
Name: default._domainkey
TYPE: TXT
Value:
"v=DKIM1;h=sha256;k=rsa;s=email;p=MIIBIjAN***IDAQAB"

**************************************************************