Add framework-specific example projects

[wwerner]

Add example projects for specific UI frameworks under examples.
Make sure these examples do not end up in the package.
Include CI builds for each example.

Research whether we can leverage Atlassian's document builder example from https://developer.atlassian.com/cloud/jira/platform/apis/document/playground/.
It would be nice to have this interactive ADF builder and see the rendered result as you change the source. Not important, but nice.

• React
• Vue
• Vanilla JS