Add option to disable a webhook

Sometimes a user might want to disable triggering webhooks temporarily.

Currently there are two ways to achieve this: The first is to delete the webhook and add it back later. This is far from ideal and additionally comes with the loss of all current log entries for the webhook.
The second is to simply uncheck all events the webhook is triggered on, and check them again when the webhook should be restored. While far better than deleting the webhook, it is still non-ideal since the user needs to remember the events that the webhook was initially triggered on.

We should add an option to set a webhook as "inactive" so that it stays an existing webhook, but will simply not get triggered on any events.