Add a DNSRPS-enabled build to regular CI pipelines

Add a DNSRPS-enabled build to regular CI pipelines

DNSRPS-enabled builds have recently been silently broken a few times due
to that feature not being tested in regular CI pipelines.  Add the
--enable-dnsrps --enable-dnsrps-dl switches to the ./configure
invocation in one of the CI jobs run for all merge requests so that
DNSRPS-related build issues can be detected in advance.

It is important to note that this change by itself does NOT enable
actual testing of the DNSRPS feature as doing that requires a DNSRPS
provider library to be present on the test host.