Align model-registry proxy cmd defaults to template defaults

[tarilabs]

Describe the bug
The model-registry proxy cmd expects defaults to MLMD gRPC on port 8081
The templates in this operator defaults to MLMD gRPC on port 9090:

model-registry-operator/config/crd/bases/modelregistry.opendatahub.io_modelregistries.yaml

Line 57 in 4c04ff7

default: 9090

The system does not e2e connects using demo

To Reproduce
Steps to reproduce the behavior:

1. Deploy operator
2. Deploy MR
3. unable to use MR

Expected behavior
Template should explicit the MLMD gRPC connection so that it accounts for the operator template defaults.
Also align to:

• [pull] main from kubeflow:main model-registry#136

Additional context
n/a