Problem

We need to find a way to add available GithubAppInstallations for a User that the user has access to for the GitHub App.

We'll have to refresh this data by hitting GitHub's API endpoint for listing a user's installations.

We may want an endpoint for this at our own /user/github-app-installations. We could also consider having this simply be available to a User on the UserView, but this may confuse things with an existing GithubAppInstallations relationship. We could perhaps rename the key to something like available-github-app-installations but keep the type github-app-installation.

Alternatively, we could also rename the user relationship in GithubAppInstallation to sender, which is more in-line with GitHub's own API and can reduce some confusion there.