ci: Introduce no-plain-errors lint rule for BE packages (no-changelog) (#7961)

## Summary
Require `ApplicationError` or its child classes instead of plain `Error`
in BE packages. This ensures the error will be normalized when reported
to Sentry, if applicable.

Follow-up to:
https://github.com/n8n-io/n8n/pulls?q=is%3Apr+is%3Aclosed+applicationerror

...

#### How to test the change:
1. ...


## Issues fixed
Include links to Github issue or Community forum post or **Linear
ticket**:
> Important in order to close automatically and provide context to
reviewers

...


## Review / Merge checklist
- [ ] PR title and summary are descriptive. **Remember, the title
automatically goes into the changelog. Use `(no-changelog)` otherwise.**
([conventions](https://github.com/n8n-io/n8n/blob/master/.github/pull_request_title_conventions.md))
- [ ] [Docs updated](https://github.com/n8n-io/n8n-docs) or follow-up
ticket created.
- [ ] Tests included.
> A bug is not considered fixed, unless a test is added to prevent it
from happening again. A feature is not complete without tests.
  >
> *(internal)* You can use Slack commands to trigger [e2e
tests](https://www.notion.so/n8n/How-to-use-Test-Instances-d65f49dfc51f441ea44367fb6f67eb0a?pvs=4#a39f9e5ba64a48b58a71d81c837e8227)
or [deploy test
instance](https://www.notion.so/n8n/How-to-use-Test-Instances-d65f49dfc51f441ea44367fb6f67eb0a?pvs=4#f6a177d32bde4b57ae2da0b8e454bfce)
or [deploy early access version on
Cloud](https://www.notion.so/n8n/Cloudbot-3dbe779836004972b7057bc989526998?pvs=4#fef2d36ab02247e1a0f65a74f6fb534e).

packages/@n8n_io/eslint-config/frontend.js

@@ -52,5 +52,6 @@ module.exports = {
 		'vue/no-side-effects-in-computed-properties': 'warn',
 		'vue/no-v-text-v-html-on-component': 'warn',
 		'vue/return-in-computed-property': 'warn',
+		'n8n-local-rules/no-plain-errors': 'off',
 	},
 };