✨ Adding WithContextFunc for webhook server to pass info to the handler

[christopherhein]

This closes #1333 and extends #549.

This non-breaking change introduces a new field on the webhook server registration, this allows you to add additional information to the request context from the ServeHTTP func. This is useful if you need to get information from the http.Request like parsing the request path for variables.

Controller Builder Implementation:

This example will write the request path back to

type pathKeyType int
const pathKey pathKeyType = iota
func setPath(ctx context.Context, r *http.Request) context.Context {
	return context.WithValue(ctx, pathKey, r.URL.Path)
}

// Get will return the new request details from the context
func getPath(ctx context.Context) string {
	return ctx.Value(pathKey).(string)
}

mgr.GetWebhookServer().Register("/webhook", &webhook.Admission{
	Handler: &fakeHandler{
		fn: func(ctx context.Context, req Request) Response {
			return Allowed(getPath(ctx))
		},
	},
	WithContextFunc: setPath,
})

Signed-off-by: Chris Hein me@chrishein.com

[k8s-ci-robot]

@christopherhein: The following test failed, say /retest to rerun all failed tests:

Test name	Commit	Details	Rerun command
pull-controller-runtime-apidiff-master	925c552	link	/test pull-controller-runtime-apidiff-master

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[christopherhein]

@vincepri re:apidiff can we ignore this? Seems like it's expected:

�[1;33minvoking: 'hack/tools/bin/go-apidiff 17b28b4c90d8736fa8ada8942235635191f85021 --print-compatible'�[0m

sigs.k8s.io/controller-runtime/pkg/webhook/admission
  Incompatible changes:
  - Webhook: old is comparable, new is not
  Compatible changes:
  - Webhook.WithContextFunc: added

[pwittrock]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: christopherhein, pwittrock

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[pwittrock]

/lgtm