fix(query-planner): fixed missing referenced variables in the `variableUsages` field

[duckki]

Fixed missing referenced variables in the variableUsages field of fetch operations

Query variables used in fetch operation should be listed in the variableUsages field. However, there was a bug where variables referenced by query-level directives could be missing in the field.

The previous PR (#2986) fixed a similar issue in fetch queries, but it didn't fully fix the issue by failing to update the variableUsages field. This PR completes the remaining issue.

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Latest commit: 1a0ba248a4129349096b2e7891df8b6ecf776f99

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 7 packages

| Name | Type | | --------------------------------------- | ----- | | @apollo/query-planner | Patch | | @apollo/query-graphs | Patch | | @apollo/federation-internals | Patch | | @apollo/gateway | Patch | | @apollo/composition | Patch | | @apollo/subgraph | Patch | | apollo-federation-integration-testsuite | Patch |

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