CI/CD: Add check for documented SSH keyfingerprints

Check works in two phases:

1. Read hosts from host.config file and retrieve current SSH fingerprints. Then, check, if these fingerprints are with documentation (file docs/access/key_fingerprints.md)
2. Check if all documented fingerprints are still valid.

Todos

• Add check in CI/CD pipeline
• Add documentation on this check

I will resolve both Todos, if you approve the check idea and implementation.