Update documentation on bastion ssh configs to use the proxycommand values

[eedgar]

[punkrokk]

@armab I'm not opposed to this. Let's see what happens with the PR (https://github.com/StackStorm/st2/pull/4881) and then we can update and make it happen.

[cognifloyd]

I just reworded some of the prose about bastion forwarding. Hopefully it fits better in the troubleshooting section now. If not, I'm not sure where else it might go. @armab and @punkrokk What do you think, is this good to merge now?

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