Add Qube Cinema EPIQ registry entries and fix related schema validation

[Andre-Lopes]

Adds Qube Cinema EPIQ to the Metadata Registry to close #1354.

Content Modifier: EPIQ

Metadata Extension:

<cpl-meta:ExtensionMetadata scope=http://www.qubecinema.com/schemas/2025/EPIQ-Metadata>
  <cpl-meta:Name>EPIQ</cpl-meta:Name>
</cpl-meta:ExtensionMetadata>

This Metadata Extension does not implement any optional Properties, and it is valid as per ST 429-16 schema.
The PR includes a fix for cplmetadataexts.schema.json as it presently requires Property Name/Value pairs.