Add Ionic extension

[damiant]

• I have read the note above about PRs contributing or fixing extensions
• I have tried reaching out to the extension maintainers about publishing this extension to Open VSX (if not, please create an issue in the extension's repo using this template).
• This extension has an OSI-approved OSS license (we don't accept proprietary extensions in this repository)

Description

This PR adds the Ionic extension.

[filiptronicek]

Hi @damiant 👋, as per our contributing guidelines:

A goal of Open VSX is to have extension maintainers publish their extensions according to the documentation. The first step we recommend is to open an issue with the extension owner. If the extension owner is unresponsive for some time, this repo (publish-extensions) can be used as a temporary workaround to ensure the extension is published to Open VSX.

The above also includes owners, who should publish the extension from their respective repositories instead of this one, so that they own the publishing process from end to end and reduce the maintenance burden on this repository.

We also have a guide on doing this via GitHub actions, which you may find useful: https://github.com/EclipseFdn/publish-extensions/blob/master/docs/direct_publish_setup.md. It is quite straight-forward to set up and enables automated publishing to not just Open VSX, but the Microsoft VS Code Marketplace as well.

Let me know if you have any questions!