chore|style: ESLint errors and warnings === 0

[kieckhafer]

Resolves #5284, #5276, #5267, #5269
Impact: major
Type: chore|style

This PR:

1. Fixes the remaining eslint warnings in our codebase, where applicable
2. Disables warnings and creates tickets for eslint issues that would require a bit more refactoring / thought, such as react/no-did-update-set-state, which will be fixed when components are updated to be functional components.
3. Removes all warning overrides in our package.json file, which now means every eslint rule we follow is now an error.
4. Removes the eslint-changed-files CI step, which is no longer needed since every rule is an error, and our classic eslint CI check takes care of all errors.

Breaking changes

None for our codebase. Any custom code might need to be updated to obey the new lint rules.

Testing

1. See that the app starts up
2. See that there are 0 errors and 0 warnings when running eslint
3. See that there are no longer any warn overrides for eslint rules in our package.json
4. See that there is no longer the eslint-changed-files CI check run on this PR

[mikemurray]

👍