Allow Users to Add Members to Groups

[GayathriVenkatesh]

Description

As of now, we don't have a feature to add members to our groups. We need to first add a user to our Allies list, after which they can add themselves to our groups.

A possible issue with this is that the allies can view all our groups, and add themselves to any of them. It could so happen that we want a user to be part of only one group, and not be able to view/join any of the others.

We could tweak this feature such that only the creator of the group can add members. This means that the Allies won't be able to view the user's groups and join them directly.
Accepting an ally invitation could mean agreeing to be a part of any of their groups. But only the creator of the group can add these allies, to give more control to the user.

cc: @julianguyen

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[Manasa2850]

@julianguyen I feel we could add a feature to the above description where we can accept/reject the group invite. This can help maintain privacy.

[julianguyen]

Hey sorry for the late reply here! I've been focusing on helping to get all our existing PRs merged.

Thanks for suggesting this feature and putting together this issue :)

I don't think we should involve ally invitations in this. But I like @Manasa2850's idea of being able to accept/reject group invites.

Based on that:

1. I think any group member should be able to send any of allies an invite to join a group.
2. We already have group leaders and they're able to create meetings and remove people from them. I think a group leader should have the power to remove members from a group.

We'll need to handle this feature very similarly to how we handle ally invitations. We'll want to send in-app notifications and emails too.

I think a good place to start is to think about how we want to design the data models.