Use the same env var for the ovn-controller as set by ovn-operator

[slawqo]

This patch renames
"RELATED_IMAGE_OPENSTACK_EDPM_OVN_CONTROLLER_AGENT_DEFAULT_IMG" to the "RELATED_IMAGE_OVN_CONTROLLER_IMAGE_URL_DEFAULT" which is the same as used by the ovn-operator to set ovn-controller image used on the control plane.
OVN requires to use same versions of the ovn-controller and ovn-northd always so using same envVar will make sure that there will be no mismatch there.

Jira: #OSPRH-1504

[openshift-ci]

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Test name	Commit	Details	Required	Rerun command
ci/prow/dataplane-operator-build-deploy-kuttl	36cef60	link	true	/test dataplane-operator-build-deploy-kuttl

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https://review.rdoproject.org/zuul/buildset/bf911770c04848fcb1341cb7694f0bc1

✔️ openstack-k8s-operators-content-provider SUCCESS in 1h 35m 23s
❌ podified-multinode-edpm-deployment-crc FAILURE in 39m 32s
❌ cifmw-crc-podified-edpm-baremetal FAILURE in 37m 58s