Restore GraphQL API with Strawberry

[callumforrester]

See #134 for details.

We have decided to put the GraphQL API back, using Strawberry GraphQL instead of graphql-core, and alongside the REST API.

Acceptance Criteria

• Running scanspec service exposes both a GraphQL and a REST API.
• The GraphQL API has the same functionality as the legacy API in GraphQL API #134
• The GraphQL API is based on Strawberry GraphQL
• The GraphQL API has tests

[callumforrester]

A note: Since we are going to try and keep the old FastAPI REST API around, it makes sense to try and make use of Strawbery's FastAPI integration if we can.