Allow self-hosted instances to prevent auto-disabling hooks

We currently automatically disable project web-hooks that fail. This has benefits for large SaaS deployments such as GitLab.com, but is disruptive for some self-hosted installations.

We want to allow self-hosted installations to easily choose to disable this feature if it gets in their way.

Proposal

Add a new ops feature flag called auto_disabling_web_hooks that administrators can use to opt-in to auto-disabling hooks.

The auto-disabling hook feature will now be disabled by default for self-managed.

Workaround to prevent autodisabling webhooks for self-managed

A patch can be applied to the GitLab instance to temporarily prevent autodisabling of webhooks #388486 (comment 1289174125).

/cc @m_gill @g.hickman