DynamicTablesPkg: Add EDK2 Core CI support

DynamicTablesPkg: Add EDK2 Core CI support

The TianoCore EDKII project has introduced a Core CI infrastructure
using TianoCore EDKII Tools PIP modules:
  * https://pypi.org/project/edk2-pytool-library/
  * https://pypi.org/project/edk2-pytool-extensions/

The edk2\.pytool\Readme.md provides information to configure the
environment and to run local builds.

This patch defines the necessary settings for enabling the Core CI
builds for DynamicTablesPkg.
 - Add DynamicTablesPkg.ci.yaml for Core CI
 - Update ReadMe.md for details and instructions

Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>
Reviewed-by: Alexei Fedorov <Alexei.Fedorov@arm.com>