Add SHA-256 and SHA-512-256 as authentication digest algorithms

Add SHA-256 and SHA-512-256 as authentication digest algorithms

* Refactored pjproject code to support the new algorithms and
added a patch file to third-party/pjproject/patches

* Added new parameters to the pjsip auth object:
  * password_digest = <algorithm>:<digest>
  * supported_algorithms_uac = List of algorithms to support
    when acting as a UAC.
  * supported_algorithms_uas = List of algorithms to support
    when acting as a UAS.
  See the auth object in pjsip.conf.sample for detailed info.

* Updated both res_pjsip_authenticator_digest.c (for UAS) and
res_pjsip_outbound_authentocator_digest.c (UAC) to suport the
new algorithms.

The new algorithms are only available with the bundled version
of pjproject, or an external version > 2.14.1.  OpenSSL version
1.1.1 or greater is required to support SHA-512-256.

Resolves: #948

UserNote: The SHA-256 and SHA-512-256 algorithms are now available
for authentication as both a UAS and a UAC.