refactor: isolate Database Lab Engine code:

* move into the separate `engine` directory:
  * DLE code (including CLI, CI Checker, common packages, etc.)
  * configuration files
  * DLE linter rules
  * Dockerfiles
  * Makefile
  * building scripts
  * SwaggerUI definitions
  * bash tests
* split GitLab CI specifications
* update GitLab CI jobs
* update .gitignore files

Author: agneum

.gitignore

@@ -1,14 +1,14 @@
 .DS_Store
 .idea/
 
-/bin/
+engine/bin/
 /db-lab-run/
 
 # Deploy contains Kubernetes configs with secrets, remove from .gitignore when generalized.
 /deploy/
 
-/configs/config.yml
-/configs/server.yml
-/configs/run_ci.yaml
-/configs/ci_checker.yml
+/engine/configs/config.yml
+/engine/configs/server.yml
+/engine/configs/run_ci.yaml
+/engine/configs/ci_checker.yml
 /packer/example.com.key