added custom broker filter

[astelmashenko]

A custom broker implementation consists of few components:

1. Feature/natsjs broker step1 #715 broker controller, to be able to specify NatsJetstreamBroker class for a broker CRD
2. added trigger controller and reconciler #716 trigger controller, to receive events for eventing triggers which are subscribed to the NatsJetstreamBroker class and reconcile subscriptions to JetStream
3. custom broker ingress #719 ingress, which accepts http requests to broker and stores it into JetStream stream storage
4. filter, which creates consumers to JetStream, get messages, filter them out and sends to targets according to triggers configuration
5. configuration is a set of yaml files describe CRD, service accounts, roles and permissions of above components
6. e2e tests/docs/examples

TODO: add description

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: astelmashenko

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[codecov]

Codecov Report

❌ Patch coverage is 4.87805% with 468 lines in your changes missing coverage. Please review.
✅ Project coverage is 27.26%. Comparing base (e77ad31) to head (24f16e2).

Files with missing lines	Patch %	Lines
pkg/broker/filter/consumer.go	0.00%	147 Missing ⚠️
pkg/broker/filter/handler.go	14.81%	138 Missing ⚠️
pkg/broker/filter/controller.go	0.00%	88 Missing ⚠️
pkg/broker/filter/reconciler.go	0.00%	65 Missing ⚠️
pkg/common/nats/conn.go	0.00%	23 Missing ⚠️
cmd/filter/main.go	0.00%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #720      +/-   ##
==========================================
- Coverage   30.81%   27.26%   -3.55%     
==========================================
  Files          53       58       +5     
  Lines        3096     3587     +491     
==========================================
+ Hits          954      978      +24     
- Misses       2074     2541     +467     
  Partials       68       68              

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