[Jenkins-42959] support ECDSA keys

[mc1arke]

Trilead currently silently ignores any ECDSA public key entries found in known_hosts, doesn't support them for identifying a remote host, and can't use ECDSA keys in user public key authentication. This change provides this support, as well as various other commits to allow some abstraction and extension of provision of key types.

[mc1arke]

@jenkinsci/code-reviewers PTAL

[paladox]

Would this be able to be merged please?

[mc1arke]

I'd ideally like a second review from someone with knowledge of SSH and/or Trilead before I merge this.

[paladox]

@mc1arke ok :), should we wait 24 hours before merging this?

[mc1arke]

A minimum of 24 hours wait is just a rough guide I follow for anything other than a simple/obvious change. For a change where I've refactored code and introduced abstractions, as well as introduced new features, I'd generally like to give as much time as possible for people to chip in. However it looks like no-one from @jenkinsci/code-reviewers it wanting to provide any particular input, and I'm unlikely to get someone just wander by and have a look so I'm likely to just proceed with merging the outstanding requests when I have time to focus on it. For instance, this pull request will break the KnownHostsTest in one of the other pull requests if I don't make changes between merges, so I need to re-test each pull before I merge them.

[paladox]

Ok thanks :)

[MarkEWaite]

I'd love to provide input, but I have other items which are more pressing right now. I won't be able to experiment with this change until next week at the earliest.

I am not an ssh expert, though I do have a wide variation of systems which I can use for various tests.

[paladox]

:)