[Feature Request] API to get invitations by user

[widavies]

It'd be nice to have an API for listing a user's current unaccepted/rejected invitations.

For example,

const user = useUser();

user.getPendingTeamInvitations(); // Lists all un-accepted/reject invitations

[widavies]

As far as I can tell, the only API to retrieve invitations is:

https://docs.stack-auth.com/next/rest-api/client/teams/list-team-invitations

This retrieves invitations for a specific team. In my application, I'd like to pull invitations for a specific user. I'd like to display a list of "pending invites" in my application.

@fomalhautb If you are okay with it, I'd like to create a PR that adds an API for pulling invitations by user.

Proposal

Add a function:

const user = useUser();
// Pulls a list of invitations for all teams the user has been invited to
user.listInvitations()