Fix duplicated yang resource references V2

Fix duplicated yang resource references V2

- Store Yang module references using SchemaSetEntity instead of SQL
- Added integration test to check number of references
- Update dispatcher for integration test to only return yang resources requested modules
- refactor schema set create & upgrade methods for better re-uses and readability
- consistent naming in related methods like(new)yangResourceContentPerName
(the name can be filename, module name or schema set name) depending on the context
- replaced 'var' with actual class names in affected classes

Issue-ID: CPS-2605
Change-Id: I8870c70832ac533bd17ce8af409a071f659e4acf
Signed-off-by: ToineSiebelink <toine.siebelink@est.tech>