Adapted...

Adapted L3_AttackMitigator/L3_CentralizedAttackDetector/L3_DistributedAttackDetector to common proto folder
- Moved imports from *.proto folder to common.proto folder
- Removed genproto.sh scripts
- Arranged requirements to accelerate Docker image creation
- Minor code and linting fixes
- Updated Dockerfile
- Arranged GitLab CI/CD pipeline