feat: add support for defining a custom list of ssh key exchange algorithms.

[Gottox]

Based on a quickfix from @zamedic, I implemented a feature that allows to define custom SSH key exchange algorithms in ArgoCD.

Allows to workaround issue #17634

Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this does not need to be in the release notes.
• The title of the PR states what changed and the related issues number (used for the release note).
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This PR adds a feature to define custom ssh key exchange algorithms. This is needed to fix #17634.

This is a first proposal and hasn't been tested in depth yet.

[todaywasawesome]

@jannfis Would you mind taking a look? Anything that touches encryption needs lots of 👀

[rouke-broersma]

@jannfis Would you mind taking a look? Anything that touches encryption needs lots of 👀

@todaywasawesome @jannfis please read the complete linked issue, there is a lot of troubleshooting in there. While this change is useful I don't believe it addresses the immediate blocker people are experiencing.

[jannfis]

Just as a heads-up, there is #18028 as the candidate to fix #17634

I will take a look at this PR later in the day :)

[Gottox]

I leave that open, as it may be useful anyway.