feat: added config option to disable suppression lists

[bennet-esyoil]

we ran into the problem that we don't want to have suppression listing. So we created a patch that disables them.

I mentioned this here: https://github.com/postalserver/postal/discussions/1575 but just decided to open a PR.

I am NOT a ruby developer so I don't know what I'm doing! :)

[willpower232]

Can you undo the unrelated changes you made to the config file?

[bennet-esyoil]

@willpower232 done. too early :upside_down_face:

[catphish]

I'm going to reject this for two reasons:

1. I believe that going forward, all such settings should be configurable per server, rather than globally.
2. This prevents suppression from soft fails, but not hard fails, which is confusing and probably a mistake. I'd be happy to accept this if both issues are addressed.