Run adapter in a context

[lionelvillard]

Proposed Changes

• receive adapter now starts in a context

Release Note

Docs

/hold need similar PR for eventing-contrib

[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/adapter/apiserver/adapter.go	80.0%	80.5%	0.5
pkg/adapter/ping/adapter.go	60.0%	84.6%	24.6

[lionelvillard]

/unhold

eventing-contrib PR: knative/eventing-contrib#1290

[aliok]

/approve
/lgtm

[knative-prow-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: aliok, lionelvillard

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[n3wscott]

Please fix sample-source

pkg/adapter/adapter.go:96:3: cannot use &Adapter literal (type *Adapter) as type adapter.Adapter in return argument:
	*Adapter does not implement adapter.Adapter (wrong type for Start method)
		have Start(<-chan struct {}) error
		want Start("context".Context) error

knative-extensions/sample-source#92