Tracking resources refactoring

[nachocano]

Fixes #1998 and others unreported bugs (e.g., Source-Trigger dependency reported by @aaron-lerner)

Proposed Changes

• Refactoring ResourceTracker to be ListableTracker, so that it can track any apis.Listable object.
• Only using ListableTracker when we need to dynamically generate informers (e.g., Channelable, KResource, AddressableType). If we know the concrete time at compile time, then use the pkg tracker.
• Avoid going to the API server every time we reconcile Channelables and Addressables. This change affects sequences, parallel, subscriptions, etc. Creating a Resource tracker used to work because we were always going to the API server instead of using the listers.
• Not using tracker for things that we own and are typed at compile time (e.g., Deployment in ApiServerSource)

Pending

• I think with this change we will be able to create the dynamic trackers only once and share them across controllers within the same process. We can do that as a follow up.

Release Note

NONE

[nachocano]

/assign @Harwayne @grantr

not ready for review yet...

[nachocano]

/assign @vaikas-google

[nachocano]

/hold need to do one more nil check

[Harwayne]

/hold need to do one more nil check

/hold

(It needs to be on its own line.)

[nachocano]

/hold need to do one more nil check

/hold

(It needs to be on its own line.)

Thanks!

/hold cancel

done the change...

[vaikas]

/approve
Thanks for doing this! Leaving lgtm for @Harwayne and @lionelvillard in case they had any additional comments.

[knative-prow-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: nachocano, vaikas-google

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[lionelvillard]

LGTM

Leaving the last LGTM to @Harwayne

[nachocano]

@Harwayne ready for another look

[Harwayne]

/lgtm

[knative-metrics-robot]

The following is the coverage report on the affected files.
Say /test pull-knative-eventing-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/duck/listable.go	Do not exist	68.9%
pkg/duck/subscriber.go	97.2%	83.7%	-13.5
pkg/reconciler/apiserversource/apiserversource.go	77.6%	77.8%	0.2
pkg/reconciler/broker/broker.go	81.2%	81.3%	0.1
pkg/reconciler/channel/channel.go	81.9%	75.9%	-6.0
pkg/reconciler/parallel/parallel.go	72.2%	71.4%	-0.8
pkg/reconciler/sequence/sequence.go	71.6%	72.4%	0.9
pkg/reconciler/subscription/subscription.go	76.7%	75.9%	-0.8
pkg/reconciler/trigger/trigger.go	85.2%	84.1%	-1.1

[lionelvillard]

@nachocano what about move listable.go over to knative.dev/pkg?

[nachocano]

@nachocano what about move listable.go over to knative.dev/pkg?

+1 yes I think it will be useful. If you have some free cycles, go for it... Otherwise I may bee able to do it in the upcoming weeks. I think we should also move Channelable. We briefly discussed that with @n3wscott sometime back...