gitlab/ci_template: run valgrind tests automatically

gitlab/ci_template: run valgrind tests automatically

Don't valgrind everything for all changes though,
but only those modules most likely to be affected
by changes in the current ci project. So, valgrind

 - gstreamer only for gstreamer core changes
 - gst-plugins-base for core/base changes
 - gst-plugins-good for core/base/good changes
 - gst-plugins-ugly for core/base/ugly changes
 - gst-plugins-bad for core/base/good changes

In other words: don't valgrind core/base if it's
good/bad/ugly that's being changed, for example.
Don't valgrind -good or -ugly for changes in -bad,
etc.

Meaning:

 - for changes in core, valgrind core/base/good/ugly/bad
 - for changes in base, valgrind base/good/ugly/bad
 - for changes in good, valgrind good/bad
 - for changes in ugly, valgrind ugly
 - for changes in bad, valgrind bad

More modules to be added later once they're valgrind
clean on the CI.

https://gitlab.freedesktop.org/gstreamer/gst-ci/merge_requests/80