* Start the webhook before informers sync.
Some webhooks (e.g. conversion) are required to list resources, so by delaying those until after informers have synced, we create a deadlock when they run in the same process. This change has two key parts:
1. Start the webhook immediately when our process starts, and issue a callback from sharedmain when the informers have synced.
2. Block `Admit` calls until informers have synced (all conversions are exempt), unless they have been designated by implementing `webhook.StatelessAdmissionController`.
Our built-in admission controllers (defaulting, validation, configmap validation) have all been marked as stateless, the main case where we want to block `Admit` calls is when we require the informer to have synchronized to populate indices for Bindings.
* Add missing err declaration
* Refactor webhook to allow adding conversion support
* pr feedback
* fix memory leak
* We can use mux.Handle
* move admission integration tests to separate file
Matt Moore
cshou
Dave Protasowski