FEATURE: Add page count as entity property

[tillprochaska]

Is your feature request related to a problem? Please describe.

• I want to be able to search for documents with a specific page count (for example only documents with more than 100 pages)
• I want to be able to view the total number of pages in search results without having to open the preview.

Describe the solution you'd like
During ingestion, add the page count as a new Pages.pageCount property.

Describe alternatives you've considered
None

Additional context
None