On new GH app installation, revalidate the installation ID cache

Currently, the installation ID cache is rebuilt once an hour by a loading cache to ensure that the IDs stay reasonably up to date. A side effect of this is that any new repositories or installations will not be visible for up to an hour until the cache is rebuilt automatically. To address this issue, a new functionality will be added to the GH webhook callback that will check events related to new installations. These calls will trigger a forced refresh of the cache to pull the new entries to reduce the potential downtime that would otherwise exist