Add replacements for manifests

[Griffin-Sullivan]

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It is difficult to deploy multiple model registries in a cluster, as there are some names that need to change in the manifest files for services and deployments.

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Use a replacements file to make it more straightforward how we expect upstream users to deploy multiple model registries in a cluster.

Describe alternatives you've considered
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Open to anything that makes multi-MR easier to set up.

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[Griffin-Sullivan]

@dhirajsb feel free to edit this to be more accurate since I'm not super familiar with the solution here