Add notification when user team invite is created

[knolleary]

Part of #4165

This is the 2rd of three PRs to introduce the new notifications system

1. Initial user notification backend #4164
2. Add notification when user team invite is created #4183 (THIS PR)
3. Rewire frontend notifications to backend notifications API #4254

Description

Adds a notification when a user is invited to a team.

The notification has type team-invite

The data of the notification contains the following data:

{
    invite: {
        id: invite.hashid
    },
    team: {
        id: team.hashid,
        name: team.name
    },
    invitor: {
        username: username
    },
    role
}

The notification includes a reference property to identify the invitation it is associated with. That allows us to clear the notification when the invite is accepted/rejected etc

[codecov]

Codecov Report

Attention: Patch coverage is 87.50000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 78.13%. Comparing base (6c9da2e) to head (b616d07).

Files	Patch %	Lines
forge/db/controllers/Invitation.js	84.61%	2 Missing ⚠️

Additional details and impacted files

@@                      Coverage Diff                      @@
##           4158-notification-backend    #4183      +/-   ##
=============================================================
+ Coverage                      77.91%   78.13%   +0.22%     
=============================================================
  Files                            292      292              
  Lines                          13389    13403      +14     
  Branches                        2996     3000       +4     
=============================================================
+ Hits                           10432    10473      +41     
+ Misses                          2957     2930      -27     

Flag	Coverage Δ
backend	78.13% <87.50%> (+0.22%)	⬆️

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[joepavitt]

invitor: {
username: username
},

typo? inviter surely?

[knolleary]

typo? inviter surely?

Yes and no. The original Invitations table has invitor (sic), as does the external api - so I've gone for consistency here. It's technically a valid spelling, albeit not common.

[Steve-Mcl]

tested on pre-staging - all good.
code review/coverage +1