chore: Migrate ESLint 8 to 9

[fhennig]

I have disabled the dependabot upgrades for ESLint 9 for now: #3057

A move from 8 to 9 will have to include migrating to the new config format.

I have decided to track this in it's own issue, so we can prioritize doing this. Not sure if it's really that important.

We need to migrate the config file and the automatic migration tool doesn't work well for .js eslintrc files, so it'll be a manual effort.

links:

• https://eslint.org/docs/latest/use/migrate-to-9.0.0
• https://eslint.org/docs/latest/use/configure/migration-guide

Tasks

• migrate to the new config format first
• then bump to the new major version

[corneliusroemer]

Thanks! I've tried this before and decided we were blocked until eslint-plugin-import supports eslint9. I had a draft PR: https://github.com/loculus-project/loculus/pull/2472/files

Turns out that support has landed now: import-js/eslint-plugin-import#2948 so we're no longer blocked!