Add initial GitLab CI support

Signed-off-by: Petr Štetiar <ynezz@true.cz>

.gitlab-ci.yml

@@ -0,0 +1,6 @@
+variables:
+  CI_TARGET_BUILD_DEPENDS: umdns
+
+include:
+  - remote: https://gitlab.com/ynezz/openwrt-ci/raw/master/openwrt-ci/gitlab/main.yml
+  - remote: https://gitlab.com/ynezz/openwrt-ci/raw/master/openwrt-ci/gitlab/pipeline.yml