add GetOtherTeam method

[johanmcos]

I'm creating a chatbot that needs to be able to get information about users' teams to decide if/how to respond to them.

As has been noted in #980, the GetTeamInfo method doesn't expose the optional team argument that the Slack API accepts, meaning my bot can only get info about its own team.

#981 attempted to fix this, but lacked backwards compatibility. This is an attempt to implement the functionality in a backwards-compatible way by creating a new GetOtherTeamInfo method, as had been suggested by @kanata2 in the discussion of #981

I'm frankly a little unsure how to implement a meaningful test for this unfortunately, but I can confirm that make pr-prep reported no issues.

[kanata2]

@johanmcos

Thanks!
Could you add GetOtherTeamInfoContext method that you can pass context.Context as an argument? 🙏

[kanata2]

GetOtherTeamInfoContext

This is put on hold as a future work.

[johanmcos]

@johanmcos

Thanks! Could you add GetOtherTeamInfoContext method that you can pass context.Context as an argument? 🙏

Sorry for the delay, I added the requested method in #1143