Add a new option 'purge-keys' to 'dnssec-policy' that will purge key
files for deleted keys. The option determines how long key files
should be retained prior to removing the corresponding files from
disk.
If set to 0, the option is disabled and 'named' will not remove key
files from disk.
(cherry picked from commit 313de3a7e2)
The keyword 'unlimited' can be used instead of PT0S which means the
same but is more comprehensible for users.
Also fix some redundant "none" parameters in the kasp test.
This commit introduces the initial `dnssec-policy` configuration
statement. It has an initial set of options to deal with signature
and key maintenance.
Add some checks to ensure that dnssec-policy is configured at the
right locations, and that policies referenced to in zone statements
actually exist.
Add some checks that when a user adds the new `dnssec-policy`
configuration, it will no longer contain existing DNSSEC
configuration options. Specifically: `inline-signing`,
`auto-dnssec`, `dnssec-dnskey-kskonly`, `dnssec-secure-to-insecure`,
`update-check-ksk`, `dnssec-update-mode`, `dnskey-sig-validity`,
and `sig-validity-interval`.
Test a good kasp configuration, and some bad configurations.
