ci: Add twister tag support to get_twister_opt

Add the ability to map file/dir paths of a PR to twister TAG.  We
introduce scripts/ci/tags.yaml to conveys which files are associated
with which tag.

Since not all file/tags will be specified in tags.yaml we use the
combination of the files modified list and the tags.yaml information to
determine which tags can be excluded (ie if the file list doesn't match
any file in tags.yaml for a given tag listed there, we can that exclude
it).

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>