Support OpenSSH formatted private keys

[felixzieger]

UniPipe crashes if it receives keys OpenSSH encoded keys with an error message similar to:

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'catalogRepository' defined in URL [jar:file:/app/unipipe-service-broker-1.0.0.jar!/BOOT-INF/classes!/io/meshcloud/dockerosb/persistence/CatalogRepository.class]: Unsatisfied dependency expressed through constructor parameter 1; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'gitHandlerService' defined in URL [jar:file:/app/unipipe-service-broker-1.0.0.jar!/BOOT-INF/classes!/io/meshcloud/dockerosb/persistence/GitHandlerService.class]: Bean instantiation via constructor failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [io.meshcloud.dockerosb.persistence.GitHandlerService]: Constructor threw exception; nested exception is org.eclipse.jgit.api.errors.TransportException: [email protected]:meshcloud/unipipe-demo.git: invalid privatekey: [B@5f233b26
	at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:800) ~[spring-beans-5.3.7.jar!/:5.3.7]
	at org.springframework.beans.factory.support.ConstructorResolver.autowireConstructor(ConstructorResolver.java:229) ~[spring-beans-5.3.7.jar!/:5.3.7]

Working on this issue could be combined with #33

[henryde]

If you tell ssh-keygen to generate a key in PEM format it will not work for current key algorithms so you will be stuck with an insecure key which will then get refused by GitHub, this is a pretty bad experience for what should be the most normal use case.