SML Markup rendering

[jaudriga]

Support mails containing JSON-LD with Schema.org data.

This adds initial support for the upcoming SML standard (see SML IETF WG and https://structured.email ) by implementing:

• schema extraction from HTML body of a mail via https://github.com/audriga/html2jsonld-php
• generic schema rendering via https://github.com/audriga/jsonld2html-cards

Note on schema extraction library: audriga/html2jsonld-php is NOT supposed to replace KItinerary. KItinerary is clearly the more powerful solution. However, KItinerary cannot be used in some Nextcloud installations (e.g. nextcloud#8322 or nextcloud#7899 ) . audriga/html2jsonld-php is supposed to be a light-weight alternative for some usage scenarios. The idea is to use html2jsonld-php only if configured.

[jaudriga]

This PR is good for having a rough outline of what we want to change. It still has some obvious open issues.

[github-actions]

Hello there,
Thank you so much for taking the time and effort to create a pull request to our Nextcloud project.

We hope that the review process is going smooth and is helpful for you. We want to ensure your pull request is reviewed to your satisfaction. If you have a moment, our community management team would very much appreciate your feedback on your experience with this PR review process.

Your feedback is valuable to us as we continuously strive to improve our community developer experience. Please take a moment to complete our short survey by clicking on the following link: https://cloud.nextcloud.com/apps/forms/s/i9Ago4EQRZ7TWxjfmeEpPkf6

Thank you for contributing to Nextcloud and we hope to hear from you soon!