Add Route to getAllWhitelisted

[klans06]

Add a route/func to get all whitelisted identity Ids for that server Id.

// getWhitelistedIds collects and stores all identity Ids associated with the server Id provided.
func getWhitelistedIds(serverId string) ([]WhitelistedRow, error) {
	rows, err := db.Query(`SELECT identity_id FROM users WHERE server_id = ?`, serverId)
	if err != nil {
		return nil, err
	}

	defer rows.Close()
}