Add --from-url for function deployment

[hwa123]

Is this a BUG REPORT or FEATURE REQUEST?:
FEATURE REQUEST
What you expected to happen:
Would be possible for kubeless function deploy to recognize the a script's github link, maybe add --from-url for that command?

[murali-reddy]

It should be possible to add the support for --from-url for kubeless function deploy. A PR would be welcomed :)

[andresmgot]

This is now available. Note that instead of having a different flag it is possible to specify an URL to the flag --from-file