librem5: Add CI

Also update it to use the template.

debian/librem5-ci.yml

+include:
+ - 'https://source.puri.sm/Librem5/librem5-ci/raw/master/librem5-pipeline-definitions.yml'
+ - 'https://source.puri.sm/Librem5/librem5-ci/raw/master/librem5-pipeline-byzantium-jobs.yml'
+ - 'https://source.puri.sm/Librem5/librem5-ci/raw/master/librem5-pipeline-common-jobs.yml'
+
+stages:
+ - package
+ - test-package