Description of problem:

If olm.bundle.object of the channel head is not set, the operator neither be found with commands 'oc get packagemanifest' nor from the web console.
"opm validate" should raise an error message.

Version-Release number of selected component (if applicable):
zhaoxia@xzha-mac operator-1 % opm version
Version: version.Version{OpmVersion:"a768ef8e8", GitCommit:"a768ef8e86e00e25fa8612dbf9f6984721449255", BuildDate:"2021-09-23T08:24:58Z", GoOs:"darwin", GoArch:"amd64"}

How reproducible:
always

Steps to Reproduce:
1. create index.yaml
zhaoxia@xzha-mac operator-1 % cat index.yaml 
---
schema: olm.package
name: operator-1
defaultChannel: alpha
---
entries:
- name: operator-1.v0.1.0
- name: operator-1.v0.2.0
  replaces: operator-1.v0.1.0
name: alpha
package: operator-1
schema: olm.channel
---
image: quay.io/xzhao/operator-1-bundle:v0.1.0
name: operator-1.v0.1.0
package: operator-1
properties:
- type: olm.gvk
  value:
    group: example.my.domain
    kind: Operator
    version: v1alpha1
- type: olm.package
  value:
    packageName: operator-1
    version: 0.1.0
schema: olm.bundle
---
image: quay.io/xzhao/operator-1-bundle:v0.2.0
name: operator-1.v0.2.0
package: operator-1
properties:
- type: olm.gvk
  value:
    group: example.my.domain
    kind: Operator
    version: v1alpha1
- type: olm.package
  value:
    packageName: operator-1
    version: 0.2.0
schema: olm.bundle

2. run "opm valiate ."
zhaoxia@xzha-mac operator-1 % opm validate .
zhaoxia@xzha-mac operator-1 % 
3.

Actual results:
"opm validate" do not raise an error message.

Expected results:
"opm validate" raise an error message to warn the author "If olm.bundle.object of the channel head is not set, the operator neither be found with commands 'oc get packagemanifest' nor from the web console."

Additional info: