Sdk: Add tab completion for fish-shell

[spboyer]

Docs: https://fishshell.com/docs/current/index.html#completion

Awesome support for current Powershell, bash and zsh. (https://github.com/dotnet/cli/blob/master/Documentation/general/tab-completion.md)

Need support for fish-shell. http://fishshell.com

[CumpsD]

I think this should do it:

complete --command dotnet --arguments '(dotnet complete (commandline -cp))'

[slang25]

@CumpsD worked great! Thank you