x/build/cmd/gopherbot: add command to ping owners of the package

[ysmolski]

It would be good to ping owners of the package in the ticket without remembering who is the owner of it. What if one could say:

@gopherbot please ping owners 
@gopherbot please ping owners to critique the solution

And then gopher would produce something like:

@name has asked @firstowner @secondowner to review this issue
@name has asked @firstowner @secondowner to critique the solution

[ysmolski]

Should this be semiautomatic? If the issue does not mention anybody and nobody has replied after 1 week then bot should trigger this automatically.

EDIT: bot should not trigger this automatically for issues that were already triaged (have according labels like NeedsFix, etc).

[agnivade]

I think this was raised earlier (the "gopherbot pinging owners automatically" part), although I can't find it now.

[ianlancetaylor]

Seems to me that once I've been mentioned in an issue, every comment on the issue sends me an e-mail. So I'm not sure what an explicit gopherbot ping command would do that isn't already done by simply commenting on the issue.