chore: disable issues and direct ppl to web-components repo [skip ci]

[vlukashov]

Description

All component-related issues (for any version of the component) should be opened either in the web-components monorepo (if it's reproducible with TypeScript and HTML, without Vaadin Flow / Java), or in the flow-components monorepo (if it's about the Java API). This repository remains open only to be able to release fixes for the versions of this web component used with Vaadin 10, 14 and Vaadin 19 for as long as they are maintained.

In order to make this clear for users, this PR

• updates the README to make the role of this repo and its relationship with the the web-components monorepo very clear
• disables new issues in this repo: any attempt to create a new issue here would direct users either to the web-components or to the flow-components monorepo

Related to: https://github.com/vaadin/components-team-tasks/issues/584

Type of change

• [ ] Bugfix
• [ ] Feature
• [x] Internal change

Checklist

• [x] I have read the contribution guide: https://vaadin.com/docs/latest/guide/contributing/overview/
• [x] I have added a description following the guideline.
• [x] The issue is created in the corresponding repository and I have referenced it.
• [ ] I have added tests to ensure my change is effective and works as intended.
• [ ] New and existing tests are passing locally with my change.
• [x] I have performed self-review and corrected misspellings.

[CLAassistant]

All committers have signed the CLA.