Added SSH over HTTPS port warning to github bootstrapping docs

[dlactin]

Added a warning for an unlikely but potential issue for folks who are using SSH over port 443 when bootstrapping flux.

I ran into this issue and even with the host keys set to the ones in that link I was unable to get this to work until I changed the port back to 22.

[kingdonb]

Sorry for the delay reviewing this! 😅

The issue being addressed isn't really clear to me, could you say a bit more about who this issue affects? How does it happen? I looked at the docs linked and it doesn't clarify the problem, or how to solve it from a Flux user perspective.

Are the affected users Enterprise GitHub customers who have set up SSH on port 443, for some firewall reason?

[dlactin]

Hello!

Not a problem.

It's been a while since I've looked at this, but from what I recall, your second comment is spot on.

Are the affected users Enterprise GitHub customers who have set up SSH on port 443, for some firewall reason?

This was implemented while a few of us were at a conference that had port 22 blocked, and it caused our attempts at bootstrapping a cluster with flux to fail without a generic host key mismatch error.

Definitely not a flux problem, but something I thought would be worth mentioning in the docs for folks bootstrapping flux this way.