Add installation_repositories.added listener to process newly added or removed repositories

[vishesh-baghel]

It is important to handle removed repositories because it may happen that the bot won't be able to fetch the details of the removed repository.
use response.repositories_added to get the list. same for removed repos.
`
"repositories_added": [
{
"id": 732309770,
"node_id": "R_kgDOK6YpCg",
"name": "lombok",
"full_name": "vishesh-baghel/lombok",
"private": false
}
],
"repositories_removed": [

],
`