refactor: setup CLI open-dkim (#4375)

Refactoring this `setup` CLI command as part of the effort to unify our DKIM feature support between OpenDKIM + Rspamd:
- Adds a `main()` method similar to other setup CLI commands.
- Help text more aligned with equivalent rspamd DKIM setup CLI command.
- DRY some repetition such as hard-coded paths to use variables.
- OpenDKIM config files are created / initialized early on now with `_create_opendkim_configs()`. `while` loop only needs to append entries, so is easier to grok.
- `_create_dkim_key()` to scope just the logic (_and additional notes_) to key generation via `opendkim-genkey`
- Now overall logic with the `while` loop of the script occurs in `_generate_dkim_keys()`:
  - Ownership fixes are now applied after the `while` loop as that seems more appropriate than per iteration.
  - Temporary VHOST config is now removed since it's no longer useful after running.
- Tests adjusted for one new log for adding of default trusted hosts content.

Overall this should be nicer to grok/maintain. Some of this logic will be reused for the unified DKIM generation command in future, which is more likely to shift towards all domains using the same keypair by default with rspamd/opendkim config generated at runtime rather than reliant upon DMS config volume to provide that (_still expected for private key_).

---------

Co-authored-by: Casper <casperklein@users.noreply.github.com>
Co-authored-by: Georg Lauterbach <44545919+georglauterbach@users.noreply.github.com>

test/tests/serial/open_dkim.bats

@@ -62,7 +62,7 @@ function teardown() { _default_teardown ; }
 
   __init_container_without_waiting
 
-  __should_generate_dkim_key 6
+  __should_generate_dkim_key 7
   __assert_outputs_common_dkim_logs
 
   __should_have_tables_trustedhosts_for_domain
@@ -78,7 +78,7 @@ function teardown() { _default_teardown ; }
   # Only mount single config file (postfix-virtual.cf):
   __init_container_without_waiting "${PWD}/test/config/postfix-virtual.cf:/tmp/docker-mailserver/postfix-virtual.cf:ro"
 
-  __should_generate_dkim_key 5
+  __should_generate_dkim_key 6
   __assert_outputs_common_dkim_logs
 
   __should_have_tables_trustedhosts_for_domain
@@ -95,7 +95,7 @@ function teardown() { _default_teardown ; }
   # Only mount single config file (postfix-accounts.cf):
   __init_container_without_waiting "${PWD}/test/config/postfix-accounts.cf:/tmp/docker-mailserver/postfix-accounts.cf:ro"
 
-  __should_generate_dkim_key 5
+  __should_generate_dkim_key 6
   __assert_outputs_common_dkim_logs
 
   __should_have_tables_trustedhosts_for_domain
@@ -113,7 +113,7 @@ function teardown() { _default_teardown ; }
   __init_container_without_waiting '/tmp/docker-mailserver'
 
   # generate first key (with a custom selector)
-  __should_generate_dkim_key 4 '1024' 'domain1.tld' 'mailer'
+  __should_generate_dkim_key 5 '1024' 'domain1.tld' 'mailer'
   __assert_outputs_common_dkim_logs
   # generate two additional keys different to the previous one
   __should_generate_dkim_key 2 '1024' 'domain2.tld,domain3.tld'
@@ -183,15 +183,15 @@ function __assert_logged_dkim_creation() {
 
 function __assert_outputs_common_dkim_logs() {
   refute_output --partial 'No entries found, no keys to make'
-  assert_output --partial 'Creating DKIM KeyTable'
-  assert_output --partial 'Creating DKIM SigningTable'
-  assert_output --partial 'Creating DKIM TrustedHosts'
+  assert_output --partial "Creating OpenDKIM config '/tmp/docker-mailserver/opendkim/KeyTable'"
+  assert_output --partial "Creating OpenDKIM config '/tmp/docker-mailserver/opendkim/SigningTable'"
+  assert_output --partial "Creating OpenDKIM config '/tmp/docker-mailserver/opendkim/TrustedHosts'"
 }
 
 function __should_support_creating_key_of_size() {
   local EXPECTED_KEYSIZE=${1:-}
 
-  __should_generate_dkim_key 6 "${EXPECTED_KEYSIZE}"
+  __should_generate_dkim_key 7 "${EXPECTED_KEYSIZE}"
   __assert_outputs_common_dkim_logs
   __assert_logged_dkim_creation 'localdomain2.com'
   __assert_logged_dkim_creation 'localhost.localdomain'