Check if we can switch from JSch to Apache Mina as JGit backend

[mbien]

while testing I noticed that most modern key standards (outside of RSA) can't be used by NB git support modules. The reason for this seems to be that JGit won't switch to the jsch fork, so we are stuck with Jsch 1.72. The original project is unmaintained since 1.55.

We could check how much work it would be to switch from jsch to apache mina, which has an extensive set of supported algorithms/ciphers/etc and is also supported by jgit.

this would require to replace JGitSshSessionFactory, this commit sets up the lib wrappers as starting point