Graphql query- fetch corpus

What does this MR do and why?

This MR adds a graphql query to fetch the Corpus records associated to a project.

Describe in detail what your merge request does and why.

How to set up and validate locally

1. Enable feature flag corpus_management
2. Create a Corpus like this. Package and project is required.

::AppSec::Fuzzing::Coverage::Corpus.create(package_id: Packages::Package.last.id, project_id: Packages::Package.last.project.id)

3. Run the following Graphql query:

query Project {
  project(fullPath:"gitlab-org/gitlab-test") {
    corpuses{
     nodes {
       id,
      	package {
      	  id
      	}
     } 
    }
  }
}

4. Response from the query should look like this:

{
  "data": {
    "project": {
      "corpuses": {
        "nodes": [
          {
            "id": 10,
            "package": {
              "id": "gid://gitlab/Packages::Package/26"
            }
          }
        ]
      }
    }
  }
}

5. Should show null if a user is not logged in

{
  "data": {
    "project": null
  }
}

Numbered steps to set up and validate the change are strongly suggested.

Database query analysis

1. Query

joins(:package).where(package: {project_id: 1})

2. Explain

explain SELECT "coverage_fuzzing_corpuses".* FROM "coverage_fuzzing_corpuses" INNER JOIN "packages_packages" "package" ON "package"."id" = "coverage_fuzzing_corpuses"."package_id" WHERE "package"."project_id" = 1

Nested Loop  (cost=0.58..30.30 rows=1 width=56) (actual time=8.015..8.018 rows=0 loops=1)
   Buffers: shared read=3
   I/O Timings: read=7.955 write=0.000
   ->  Index Only Scan using idx_installable_helm_pkgs_on_project_id_id on public.packages_packages package  (cost=0.43..4.02 rows=34 width=8) (actual time=8.012..8.013 rows=0 loops=1)
         Index Cond: (package.project_id = 1)
         Heap Fetches: 0
         Buffers: shared read=3
         I/O Timings: read=7.955 write=0.000
   ->  Index Scan using index_coverage_fuzzing_corpuses_on_package_id on public.coverage_fuzzing_corpuses  (cost=0.15..0.72 rows=5 width=56) (actual time=0.000..0.000 rows=0 loops=0)
         Index Cond: (coverage_fuzzing_corpuses.package_id = package.id)
         I/O Timings: read=0.000 write=0.000

3. Visualization

https://console.postgres.ai/gitlab/gitlab-production-tunnel-pg12/sessions/7069/commands/24958

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #341486 (closed)