Resolve "Add missing YANG configuration knobs for the Kea 2.4.0 release"

Closes #2832 (closed).

• 75586d06 add missing YANG nodes

  • allocator
  • ddns-ttl-percent
  • exclude-first-last-24,
  • ignore-dhcp-server-Identifier
  • offer-lifetime
  • pd-allocator
  • read-timeout
  • tcp-user-timeout
  • write-timeout

  Removed obsolete YANG nodes: contact-points, keyspace.

• 9930316d remove LIBYANG_VERSION and SYSREPO_VERSION

  They were not used and they were not properly expanded in config.h anyway. They showed up as:

  /* libyang version */
  #define LIBYANG_VERSION "${LIBYANG_VERSION}"
  
  /* sysrepo version */
  #define SYSREPO_VERSION "${SYSREPO_VERSION}"

• 3914e691 add libyang-cpp and sysrepo-cpp flags to distcheck

• 514ad4ef add ChangeLog entry