This commit converts the license handling to adhere to the REUSE
specification. It specifically:
1. Adds used licnses to LICENSES/ directory
2. Add "isc" template for adding the copyright boilerplate
3. Changes all source files to include copyright and SPDX license
header, this includes all the C sources, documentation, zone files,
configuration files. There are notes in the doc/dev/copyrights file
on how to add correct headers to the new files.
4. Handle the rest that can't be modified via .reuse/dep5 file. The
binary (or otherwise unmodifiable) files could have license places
next to them in <foo>.license file, but this would lead to cluttered
repository and most of the files handled in the .reuse/dep5 file are
system test files.
Add a Pytest based system test for the 'checkds' feature. There is
one nameserver (ns9, because it should be started the latest) that
has configured several zones with dnssec-policy. The zones are set
in such a state that they are waiting for DS publication or DS
withdrawal.
Then several other name servers act as parent servers that either have
the DS for these published, or not. Also one server in the mix is
to test a badly configured parental-agent.
There are tests for DS publication, DS publication error handling,
DS withdrawal and DS withdrawal error handling.
The tests ensures that the zone is DNSSEC valid, and that the
DSPublish/DSRemoved key metadata is set (or not in case of the error
handling).
It does not test if the rollover continues, this is already tested in
the kasp system test (that uses 'rndc -dnssec checkds' to set the
DSPublish/DSRemoved key metadata).
