feat(api): simplify discussions enrichment and use graphql-codegen for types

[setchy]

This PR focuses on a few long standing improvements.

• Use of graphql-codegen to generate types for GitHub GraphQL request/response shapes - closes #985
• Refactor discussions enrichment query to use query > repository > discussion instead of query > search for a more targeted discussion result based on repo + discussion number

This also setups up the ground work for further enhancements that will be in separate follow-up PRs. Examples of this include refactoring the issue and pull request enrichment calls from REST to GraphQL, which will have a positive impact on reducing our use of API rate limits.

[sonarqubecloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
94.4% Coverage on New Code
0.0% Duplication on New Code

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