Deprecation: renames Container Registry estimation flag name

Be sure to link this MR to the relevant deprecation issue(s).

• Deprecation Issue: #416509 (closed)

What does this MR do and why?

Renames GraphQL field registry_size_estimated to be more aligned with its "base" field container_registry_size

- registry_size_estimated
+ container_registry_size_is_estimated

Related to #413907

Screenshots or screen recordings

N/A

How to set up and validate locally

Open a GraphQL explorer (http://localhost:3000/-/graphql-explorer) and run a query:

query getNamespaceStorageStatistics($fullPath: ID!) {
  namespace(fullPath: $fullPath) {
    id
    name
    storageSizeLimit
    actualRepositorySizeLimit
    additionalPurchasedStorageSize
    totalRepositorySizeExcess
    totalRepositorySize
    containsLockedProjects
    repositorySizeExcessProjectCount
    rootStorageStatistics {
      storageSize
      repositorySize
      lfsObjectsSize
      containerRegistrySize
      containerRegistrySizeIsEstimated
      buildArtifactsSize
      packagesSize
      wikiSize
      snippetsSize
      __typename
    }
  }
}

with vars like:

{
  "fullPath": "h5bp"
}

MR acceptance checklist

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