Add a way to get SSH debug info for flux bootstrap

[ambis]

Describe the bug

I've had multiple times when there has been some problem with flux bootstrap git and ssh. So far, it has always been my fault-ish.

But the problem is, there is no way (AFAIK) to get flux tell you exatly what is up.

Problems I have encountered (which I've solved eventually, but with zero help from flux):

• Too many SSH keys in my (forwarded) agent, even though my server user config has Host *\n\tIdentitiesOnly yes and I've verified it with verbose (ssh git@gitlab.com -vvv works like a charm)
• I had an old SSH host key to internal GitLab my known_hosts file from years back (above the more current one, both were valid but the other was of older key variant)
• (There was a third case but just cannot get it into my head right now)

The first of these issues were from flux 0.13.4, others were from a bit earlier versions.

Could you PLEASE add an option to get more SSH debug info from flux's ssh operations? Especially as there appers to be often problems in cases where the current SSH config for the user works just fine using plain ssh (so you really cannot debug these other than with trial and error).

[ambis]

BTW, this was the error I got for the first case in list above.

root@myhost:~#  flux bootstrap git  --components-extra=image-reflector-controller,image-automation-controller --url=ssh://git@gitlab.com/me/repo.git --branch prod --path clusters/prod
► cloning branch "prod" from Git repository "ssh://git@gitlab.com/me/repo.git"
✗ failed to clone repository: unknown error: remote:

So.. yeah.

This got solved by clearing my agent from all other keys and adding only my gitlab key.

[cbl315]

Any update about this issue?