Add .gitlab-ci.yml and pre-cache script (#14)

* add .gitlab-ci.yml and pre-cache script

* fix fmt and clippy

* ci: fix deny

* ci: fix deny

* add unleash

* Update .gitlab-ci.yml

Co-authored-by: Squirrel <[email protected]>

* unleash on k8s runner

* switch all jobs to k8s runner

* removed pre_cache script

* add image to k8s template

* returned docker executor back

Co-authored-by: Squirrel <[email protected]>