fix(lint): migrate to eslint v9 + flat config + recommended rules

[gdostie]

This pull request does the following improvements to our ESLint configuration:

• Update to major version 9
• Update other dependencies related to ESLint (like plugins) to their latest version
• Migrate our configuration to flat config (new recommended config format)
• Activate the recommended configurations from eslint and typescript-eslint
• Ensure we have a green CI by either fixing newly discovered errors or disabling them
• Stop running ESLint through Jest, ESLint now runs on test files by itself when running lint or lint:fix

Note to the reviewers for discussion:

• I tagged these changes as breaking as a preventive measure since some types have become stricter than they were. For instance, any isn't accepted explicitly as a valid type anymore, so I had to narrow it down to something more meaningful.
• There are a lot of usage of any that I simply let it be and disabled the rule, because I don't have enough knowledge of the feature itself to assert the correct type. Perhaps we could let this branch live longer and work on fixing them all before merging? Or merge as is and continue like that.
• This is a really big PR, take your time to read it. This change was done as a side project and can be kept alive until we are truly satisfied with the new state. A lot of changes have been automatically fixed by ESLint itself, but some errors required manual intervention.

Acceptance Criteria

• My changes are publicly available, documented, and deployed in production. (i.e. on Swagger)
• JSDoc annotates each property added in the exported interfaces
• The proposed changes are covered by unit tests
• Commits containing breaking changes a properly identified as such
• README.md is adjusted to reflect the proposed changes (if relevant)
• My merge commit message will be conventional (See Conventional Commit)

[github-actions]

🎉 This PR is included in version 56.0.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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