refactor: clean up `apollo_federation::compile_service`

[tusharmath]

Minor clean ups required:

Current Implementation

pub fn compile_service(config: &ConfigModule) -> Valid<IR, String> {
    let mut sdl =
        crate::core::document::print(filter_conflicting_directives(config.config().into()));

    writeln!(sdl).ok();
    // Add tailcall specific definitions to the sdl output
    writeln!(
        sdl,
        "{}",
        crate::core::document::print(filter_conflicting_directives(Config::graphql_schema()))
    )
    .ok();
    writeln!(sdl).ok();
    // Mark subgraph as Apollo federation v2 compatible according to [docs](https://www.apollographql.com/docs/apollo-server/using-federation/apollo-subgraph-setup/#2-opt-in-to-federation-2)
    // (borrowed from async_graphql)
    writeln!(sdl, "extend schema @link(").ok();
    writeln!(sdl, "\turl: \"https://specs.apollo.dev/federation/v2.3\",").ok();
    writeln!(sdl, "\timport: [\"@key\", \"@tag\", \"@shareable\", \"@inaccessible\", \"@override\", \"@external\", \"@provides\", \"@requires\", \"@composeDirective\", \"@interfaceObject\"]").ok();
    writeln!(sdl, ")").ok();

    Valid::succeed(IR::Service(sdl))
}

Technical Requirements

• Add new snapshot tests for compile_service before making the change.
• Ensure there is only one writeln! statement and one call to document::print.
• Create one ServiceDocument and modify it with definititions that are required or need to be dropped.
• Ensure the new tests pass with the new change.
• NOTE: rename file apollo_federation to federation

[tusharmath]

/bounty $50

[algora-pbc[bot]]

~~## 💎 $50 bounty • Tailcall Inc.~~

~~### Steps to solve:~~ ~~1. Start working: Comment /attempt #2904 with your implementation plan~~ ~~2. Submit work: Create a pull request including /claim #2904 in the PR body to claim the bounty~~ ~~3. Receive payment: 100% of the bounty is received 2-5 days post-reward. Make sure you are eligible for payouts~~

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Attempt	Started (GMT+0)	Solution
🟢 @ayusham001	Sep 25, 2024, 3:47:10 AM	WIP

[ayusham001]

/attempt #2904

Algora profile	Completed bounties	Tech	Active attempts	Options
@ayusham001	1 tailcallhq bounty + 8 bounties from 3 projects			Cancel attempt

[Abiji-2020]

@ayusham001 is this still on shall i work on it too?

[ayusham001]

@ayusham001 is this still on shall i work on it too?

Yep, you can start working on it

[github-actions[bot]]

Action required: Issue inactive for 30 days. Status update or closure in 7 days.

[github-actions[bot]]

Issue closed after 7 days of inactivity.