Operator installed Namespace dropdown should always be enabled and user can choose from the full set of namespaces

Description of problem:

During an operator installation with the Installation mode set to all namespaces, the "Installed Namespace" dropdown selection is restricted to "openshift-operators" or another specific namespace, if one is recommended by the operator owners.

With to recent* change to allow non-latest operator version installs, users should be allowed to select any namespace to install a globally installed operator.

Related info:
Operators can now be installed on non-latest versions with the merge of * https://github.com/openshift/console/pull/12743 They require a manual approval and because of the way InstallPlan upgrades work, this effects all operators installed that namespace. 

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