log: adjust level and message(s) slightly for four messages

[georglauterbach]

Description

Small follow-up where I found some log levels that I thought should be changed. Disabling ClamAV and SA is perfectly fine, and should not be logged with the same level as something like Welcome to docker-mailserver <VERSION>. Another small adjustment to the SSL insecure message, nothing big though. I swear this is the last log adjustment PR in a while :D

Type of change

• Improvement (non-breaking change that does improve existing functionality)

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (README.md or the documentation under docs/)
• If necessary I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes