Add htmlAttributes to UmbracoRichText and upgrade to Vitest 2

[thebuilder]

• Adds support for setting default attributes that are forwarded to specific HTML elements, based on tag.
  • The className will be merged instead of overwritten.
• Upgrade the project to Vitest 2, and use browser mode for tests
• Use pnpm workspace, to avoid pnpm complaining about the examples projects.

The StackBlitz project is broken because of this change. Doesn't seem to start correctly with pnpm.
But if we don't run everything as workspace, the version for the example package is also going to be locked.