fix(federation): removed RebaseError::InterfaceObjectTypename error

[duckki]

Summary

• The rebase_on method was prohibiting __typename field from being rebased on an interface object type by raising InterfaceObjectTypename error.
• But, it seemed unnecessarily prohibitive, rejecting plannable queries.
• Although it's odd to fetch __typename from interface object types, there are already several other cases where such __typename selections are added to interface object types.
• Such __typename selections are benign and we currently don't plan to remove all of those cases at this time.
• Thus, this PR removes the error variant and the check for the error altogether.
• Also, added a regression test that caused the error previously.

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Checklist

Complete the checklist (and note appropriate exceptions) before the PR is marked ready-for-review.

• PR description explains the motivation for the change and relevant context for reviewing
• PR description links appropriate GitHub/Jira tickets (creating when necessary)
• Changeset is included for user-facing changes
• Changes are compatible[^1]
• Documentation[^2] completed
• Performance impact assessed and acceptable
• Metrics and logs are added[^3] and documented
• Tests added and passing[^4]
  • Unit tests
  • Integration tests
  • Manual tests, as necessary

[apollo-librarian]

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File Changes

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* graphos/routing/(latest)/observability/telemetry/instrumentation/standard-instruments.mdx

Build ID: 1c21cb2641fbdaed17b06fde
Build Logs: View logs

URL: https://www.apollographql.com/docs/deploy-preview/1c21cb2641fbdaed17b06fde

[sachindshinde]

This is fine given our current limitations of interface object handling; for folks who may not know why we need to do this, see this comment from a previous PR.

Note that this change cannot be mirrored to the JS codebase as-is, as the JS codebase still implements the fragment-reuse optimization which uses errorIfCannotRebase: false, and that codepath needs __typename to be "skipped" to prevent the issue described in this federation repo PR. This fragment-reuse codepath was removed from the Rust codebase, so it's fine here.