handle operator namespace could be optional in OperandRegistry

[YCShen1010]

Fix bug for missing operator ns when retrieving CatalogSource from packagemanifest to address the ODLM permission issue
issue: https://github.ibm.com/IBMPrivateCloud/roadmap/issues/60042

Verified

1. create keycloak operator in OperandReigstry without namespace

   - channel: stable
     installPlanApproval: Automatic
     name: edb-keycloak
     packageName: cloud-native-postgresql
     scope: public
   

2. get pending status for keycloak operandrequest

   status:
     members:
       - name: keycloak-operator
         phase:
           operandPhase: Not Found
           operatorPhase: Not Found
     phase: Pending
   

3. error msg in ODLM pod log

   E0821 04:58:58.540533 1 reconcile_operator.go:87] Failed to get suitable OperandRegistry keycloak-simple/keycloak-registry: packagemanifests.packages.operators.coreos.com "cloud-native-postgresql" is forbidden: User "system:serviceaccount:keycloak-simple:operand-deployment-lifecycle-manager" cannot list resource "packagemanifests" in API group "packages.operators.coreos.com" at the cluster scope
   E0821 04:58:58.541656 1 operandrequest_controller.go:148] failed to reconcile Operators for OperandRequest keycloak-simple/keycloak-request: packagemanifests.packages.operators.coreos.com "cloud-native-postgresql" is forbidden: User "system:serviceaccount:keycloak-simple:operand-deployment-lifecycle-manager" cannot list resource "packagemanifests" in API group "packages.operators.coreos.com" at the cluster scope
   E0821 04:58:58.551331 1 operandconfig_controller.go:83] failed to update the status for OperandConfig keycloak-simple/keycloak-registry : packagemanifests.packages.operators.coreos.com "cloud-native-postgresql" is forbidden: User "system:serviceaccount:keycloak-simple:operand-deployment-lifecycle-manager" cannot list resource "packagemanifests" in API group "packages.operators.coreos.com" at the cluster scope
   

4. fix the code, opreq status comes back to running.
   test image: quay.io/yuchen_shen/odlm:opreg_optn

[Daniel-Fan]

/retest

[Daniel-Fan]

/retest

[Daniel-Fan]

/lgtm

[ibm-ci-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Daniel-Fan, YCShen1010

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