Update to ESLint 9

[coliff]

We're currently using ESLint v8.57.1 which is deprecated and no longer updated.

• Update ESLint to latest version and install
• Update config file to recommended format (https://eslint.org/docs/latest/use/configure/configuration-files)
• Remove .eslintignore file (since ignored files can be in the new config file)
• Make sure ESLint tests pass successfully

[aitheenti]

@coliff I can work on this if you're still looking for help.

[coliff]

@coliff I can work on this if you're still looking for help.

Yep, sure.. if you have experience with this then please go ahead!