Current job triggers based on matching of changed paths is quite
limited, so lets make it possible to additionally trigger manual CI jobs
by adding CI specific pull request build labels:
* `ci:target:x86:64` label is going to trigger CI target check jobs for
x86/64 (sub)target.
* `ci:kernel:x86:64` label is going to trigger CI kernel check jobs for
x86/64 (sub)target.
Signed-off-by: Petr Štetiar <ynezz@true.cz>
