Render notification progress update as html

[msujew]

What it does

Closes #10587
Addresses one issue from #10579

Renders the message of a progress update also to html. Additionally, allows to include unknown protocols in hrefs, which previously lead to command:some-command hrefs from being removed by DOMPurify.

How to test

1. Install the RedHat Java extension and open a Java Project.
2. Wait until the "Opening Java Projects" notification appears.
3. Click the link, "check details", which should run the java.show.server.task.status command. (be fast, the notification disappears quite quickly)

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[colin-grant-work]

The changes look good to me and resolve the issue described.