50 implement resolvers and connect graphql to mysql

[agnesas]

Description

Set up the GraphQL API for the Pokémon application and connect it to the MariaDB/MySQL database. This PR includes the GraphQL server and initial schema from #49, as well as the resolvers, Apollo Client integration, and frontend data fetching from #50.

The React frontend can retrieve Pokémon data through the GraphQL API, and the backend includes error handling for failed database queries. The README has also been updated with backend setup and configuration instructions.

Changes

• Set up an Apollo Server with an initial GraphQL schema and queries.
• Connect GraphQL resolvers to the MariaDB/MySQL database.
• Implement queries for retrieving all Pokémon and retrieving a Pokémon by ID.
• Configure Apollo Client in the React frontend.
• Display Pokémon data retrieved from the GraphQL API.
• Handle loading states, failed queries, and missing Pokémon.
• Mask internal GraphQL errors to avoid exposing database details and stack traces.
• Document backend installation, database configuration, startup, and example queries in the README.

Testing

• Verified that the backend builds and starts successfully on the VM without Docker.
• Verified that GraphQL queries retrieve Pokémon data from the database.
• Verified that querying a nonexistent Pokémon returns null.
• Verified that the frontend displays data retrieved through GraphQL.
• Tested database authentication failure and confirmed that the response does not expose internal database details or stack traces.
• Verified that the backend works normally again with valid database credentials.

---

Issue

Closes: #48, which includes #49, #50, #51 and #52

[larsjfo]

Overall we have a lot of conflicts between this PR and #55. We have to make sure both PR's work well together. I suggest merging #55 first, then rebase main into 50-implement-resolvers-and-connect-graphql-to-mysql. Afterward we can make sure everything works as expected.

[larsjfo]

LGTM, great work!