Migrate to ESLint v9

[fargito]

Clear and concise description of the problem

Merges are currently broken because our CDK generated services are not using the eslint v9 flat config

Suggested solution

Use the flat config: https://eslint.org/docs/latest/use/configure/migration-guide

Alternative

No response

Additional context

No response

Validations

• [X] Read the Contributing Guidelines.
• [X] Read the docs.
• [X] Check that there isn't already an issue that request the same feature to avoid creating a duplicate.

[fargito]

Update: typescript-eslint does not yet support eslint v9. We'll wait till they do before updating. Tracking issue: https://github.com/typescript-eslint/typescript-eslint/issues/8211

[fargito]

In the meantime, I'll limit the generated version of eslint to 8

[fargito]

In #1146 the generation issue should be temporarily fixed, before implementing the long-term fix: the migration to eslint v9