Add ssh-ed25519 and ecdsa-sha2-nistp256 algorithms to ManuallyProvidedKeyVerificationStrategy SSH key help text

[kryachkov]

Currently ManuallyProvidedKeyVerificationStrategy SSH key help text only mentions ssh-rsa and ssh-dss while ssh-ed25519 and ecdsa-sha2-nistp256 are supported too. It made me spend too much time trying to debug why Jenkins could not establish connection using ssh-rsa key, while it was using ssh-ed25519 and I had no idea I can put ssh-ed25519 key there.

Testing done

Don't think there is much to test

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