Federation @join__field requires parameter handling improvement

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- [ ] 1. The issue provides a reproduction available on Github, Stackblitz or CodeSandbox
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- [ ] 2. A failing test has been provided
- [ ] 3. A local solution has been provided
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---

**Describe the bug**

Given this snipped from a working supergraph schema.

```graphql
type Environment {
id: ID!
}

type Whatever {
id: ID!
environment: Environment! @join__field(graph: ACCOUNTS) @join__field(graph: LOCAL, external: true)
external1: String @join__field(graph: LOCAL, requires: "id environment {id}")
external2: String @join__field(graph: LOCAL, requires: "id environment{id}")
}
```

The resolver for `external1` will receive the `required` fields correctly. But `external2` will get only the `id` field correctly filled. The difference is only the space.

Not sure what is the best way to fix this, but i assume this is driven from [utils/getKeyFnForFederation](https://github.com/ardatan/graphql-tools/blob/4b56b04d69b02919f6c5fa4f97d33da63f36e8c8/packages/federation/src/utils.ts#L12C17-L12C38). The function considers the first level keys (split by space) only.

I think we have 2 options:
* keep current simple logic and split the key until first `{` - will still give you the whole subtree (might be more data than needed)
* we could parse the whole selectionSet and recursively filter the root value.

Read packages/federation/src/utils.ts, especially getKeyFnForFederation, and reproduce the two requires selection sets from the issue. Determine how nested fields with different whitespace are handled; done means external2 receives the nested environment id as external1 does, with coverage for the reported difference.

Written by the indexing model from the issue text.