`starport version`: output go version, uname and PATH

[fadeev]

Is your feature request related to a problem? Please describe.
When users submit issues we ask them to run starport version, go version, uname -a and we often need to ask for their PATH.

Describe the solution you'd like
Instead, why don't we output all of this information with starport version.

% starport version
Starport: v0.15.1 darwin/amd64 -build date: 2021-04-01T08:17:55Z
Go: go version go1.16 darwin/amd64
System: Darwin system.local 20.4.0 Darwin Kernel Version 20.4.0: Fri Mar  5 03:57:04 PST 2021; root:xnu-7195.101.1~4/RELEASE_X86_64 x86_64
Path: /Users/fadeev/.cargo/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/MacGPG2/bin:/Library/Apple/usr/bin:/Users/fadeev/go/bin

[ilgooz]

This is probably not relevant after #1215.

[fadeev]

Maybe not path, go and system still are I think. All the debug info we need under version command.

[ilgooz]

Even if we print path, there is no fixed way of telling that if user has added it's go bin to the PATH because go bin path's name can be anything.

Another way of checking this is actually installing (takes under a second) a dummy main program with a unique binary name and checking if it can be found in any of the paths defined in PATH. This check can be performed when you run any of the starport commands and if it's not set, starport can exit and print a link to docs related to it.

[fadeev]

@ilgooz this is a great idea! I suppose we don't have to exit, though, a warning should be sufficient.