SPA demo essentials plugin breaks the project

SPA demo essentials plugin causes warning and produces invalid project.

Reason:
`hst:allowedorigins` should be added on a virtual host node level but it has been added on the mount node:

• https://code.onehippo.org/cms-community-dev/hippo-essentials/blob/release/14.2/plugins/spa-demo/src/main/java/com/onehippo/cms7/essentials/plugins/spademo/SpaDemoInstruction.java#L57

Reproduction path:

• Follow instructions from the documentation page: https://documentation.bloomreach.com/14/library/concepts/spa-integration/demo-projects.html
• Start the project.

Actual:

• CMS produces a warning about not supported `hst:allowedorigins` property.
• All the properties under `hst:allowedorigins` are not imported.

Expected:

• CMS uses `hst:allowedorigins` property to generate a correct `Access-Control-Allow-Origin` response header.

The fix should be backported to 14.1.