Description

• Change the default dkim-signing.conf
  • support multiple domains with a single "path" line
  • support optional selector_map
• Changes to setup config dkim (rspamd-dkim) to support the above
• Refactor the rspamd DKIM documentation to simplify the common scenarios (multiple domains, single selector, migrating keys from opendkim)

Related issues:

• [Proposal] ease migration of keys from opendkim to rspamd (and better support multiple domains) #4649 was my original motivation (where I discussed this with @polarathene)
• [TODO]: Consider rspamd DKIM config to use selector_map #3778 is addressed by this as well (including many of the incidental improvement ideas within that thread)

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Improvement (non-breaking change that does improve existing functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my 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 modified tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have added information about changes made in this PR to CHANGELOG.md