Resolve "CI: check for duplicate and unused messages"

Closes #1723 (closed).

• 7f29ae2e tools/check-messages.sh

• cbbcf06e fix a problem with bandit searching .git

• 890f97fc tools/check-messages.py

• 5932a8df fix placeholder ids in messages

• d081f180 exhonerate existing duplicate messages

• d3441df7 rm tools/check-messages.sh

• 2927a0ec add debug levels to message documentation

• 44fb62ca remove unlogged message definitions

• bfaf63be regenerate messages

CI run before fixing the reported errors: https://gitlab.isc.org/isc-projects/kea/-/jobs/4450693.