Add ecm:pos as a range element index in MarkLogic

Since NXP-24530, ecm:pos is required on tree_children page provider.

We need to add this property as a range element index in Marklogic. Indeed, without this setup, MarkLogic won't be able to perform the request and will return an error.

• We need to add this settings in the addons + marketplace package (with that repository will know how to deal with this sorting property)
• We need to add this property in our documentation in order to create the index on MarkLogic side
• We need to check benchmark and MarkLogic setup and add needed things