Eslint flat config

[SimonFischer04]

PR Checklist:

• Provide a meaningful description to this PR or mention which issues this fixes.
• Ensure the project builds with npm run build
• Add tests for your change. This includes negative tests (i.e. inputs that need to fail) as well as baseline tests (i.e. how should the directory structure look like?).
• Run the test suite with npm test
• If there are baseline changes, review them and make a separate commit for them with the comment "accept baselines" if they are desired changes
• If you added a required option, also add it to the template creation (.github/create_templates.ts)
• Add a detailed migration description to docs/updates explaining what the user needs to do when manually updating an existing project
• Add your changes to CHANGELOG.md (referencing the migration description and this PR or the issue you fixed)

Description:
add description here

[SimonFischer04]

work in progress version of moving root eslint config to new flat config format.:
basic config / migrated rules from .eslintrc.js && .eslintignore to eslint.config.js
NOTE: prettier plugin still missing
PS: kept old configs as .bak for now / as reference until is pr is done

Sorry, not much for now, as I spent most time reading README / dev setup and debugging issue described on discord, this is also why I ultimately started with migrating the root config and not the template - as I could not get the generator to run - should still be useful as reference / can be copied to the template later.

Will (hopefully) have time tomorrow to continue this.

[SimonFischer04]

NOTE for docs:
for the vs-code users: you may have to enable the new format to get linting help in ide working again:

[SimonFischer04]

another thing:
would it make sense to create a shared "eslint-config-iobroker" (more details see: https://eslint.org/docs/latest/extend/shareable-configs)
with the 4 common templates (space/singlequotes, space/doublequotes, tab/doublequote, tab/sinlgequote)?
so if changes are required (again) not every adapter has to do (a lot of) migration.

[AlCalzone]

I'm afraid we cannot upgrade yet:
typescript-eslint/typescript-eslint#8211
Until typescript-eslint supports ESLint v9, we can neither upgrade the creator, nor can we upgrade TS adapters. Upgrading JS-only adapters only will create a mess I'm not willing to support.
So we should wait and tell devs not to merge ESLint v9 PRs.

For reference: Here's documentation about the necessary changes to the configuration files:
https://eslint.org/blog/2022/08/new-config-system-part-2/