gitlab-ci: Use template files from developer tools

Using templates simplifies our Gitlab CI configuration.
You can overwrite the template or implement own pipeline
(ignoring the template).

Developer tools project is added as a submodule. We depend on
this project in our CI, tools like pre-commit.

We maintain this submodule to be always up to date (auto bot will
be part of developer tools - updating all dependencies when there
is a new version).

Signed-off-by: Martin Kojtal <martin.kojtal@arm.com>