* Improve and link Network Proxy docs
It is possible for proxy issues to cause "unable to open shell", so
detail there.
Having the "how-to" in the debug page makes more sense than on the
porting page, so move it.
Fixed a few formatting issues at the same time.
* Edits
* typo
Fixes#29060
Allow delegate_to if transport is either nxapi or eapi.
Persistent connection uses `cli` transport and create
a local socket on control node. Hence delegate_to is not allowed
for `cli` transport.
However as `nxapi` and `eapi` transport does not use persistent connection
it is possible to use delegate_to in this case.