feat: support file upload in router

[pedraumcosta]

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Motivation and Context

This PR makes possible to support a file upload according to spec:

https://github.com/jaydenseric/graphql-multipart-request-spec

This PR depends on this PR from graphql-go-tools:

https://github.com/wundergraph/graphql-go-tools/pull/758

This PR parse multiform part http requests with files, saves in the file system and passed the file information along the graphql tools library to be forwarded to a subgraph that supports files uploads. In order to make tests possible, I added file uploads operations to the demo employee subgraph and some enhanced methods to test infrastructure.

TODO

• [X] Tests or benchmark included
• [ ] Documentation is changed or added on https://app.gitbook.com/
• [X] PR title must follow conventional-commit-standard