Set Ingress status with reason when reconcile failed

[nak3]

As per title, this patch changes to set Ingress status with reason when reconcile failed.

After this patch controller sets the status as below:

$ kubectl get dm
NAME                                        URL               READY     REASON
domainmapping.serving.knative.dev/foo.com   https://foo.com   Unknown   ReconcileIngressFailed

$ kubectl get king foo.com 
NAME      READY     REASON
foo.com   Unknown   ReconcileIngressFailed

$ kubectl describe dm foo.com
  ...
    Message:               failed to translate ingress: failed to fetch secret: secret "invalid-secret" not found
    Reason:                ReconcileIngressFailed
    Status:                Unknown
    Type:                  IngressReady

Fix #790

[nak3]

I will add unit test later (separate PR) as it needs a lot of work due to #145

[codecov]

Codecov Report

Merging #791 (96968a2) into main (55ad3b3) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #791   +/-   ##
=======================================
  Coverage   73.16%   73.16%           
=======================================
  Files          18       18           
  Lines         749      749           
=======================================
  Hits          548      548           
  Misses        165      165           
  Partials       36       36           

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[nak3]

/cc @ZhiminXiang @carlisia

[ZhiminXiang]

/lgtm

[knative-prow-robot]

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