team: grant team lead maintainer permissions on github team

[DConnorFong]

Summary

Could be a bug but I am not too sure what the intended behavior is

Requirements

Steps:

1. /rocket team create $TEAM --lead $YOU --channel $CHANNEL
2. Under $YOU I tag myself in Slack
3. Generate the team

Expected:
I would be a maintainer of the newly generated team

Actual:
I am not

Context

This seems like a good step to automate as it contributes to a pain point of organization owners having to manually set this up for me.

[bobheadxi]

Actual:
I am not

💯

Context on what a team maintainer is: https://docs.github.com/en/free-pro-team@latest/github/setting-up-and-managing-organizations-and-teams/giving-team-maintainer-permissions-to-an-organization-member

[chuck-sys]

We may want to either change the GithubInterface to include a add_team_maintainer() function, or we can append another parameter to GithubInterface.add_team_member(). Both seem fine.

For the person who implements this in the near future: https://pygithub.readthedocs.io/en/latest/github_objects/Team.html?highlight=add_membership#github.Team.Team.add_membership

https://developer.github.com/v3/teams/members/#parameters