Add option to pass typoscript to customDimensions

This change enables the use of straight up typoscript in the _getValue function. 
This should not affect the excisting functionality in any way.

Working example using this functionality:
```
plugin.tx_twgoogleanalytics.settings.customDimensions{
	dimension1 = USER
	dimension1 {
		userFunc = Bolius\BoliusProducts\Service\ProductService->getProductPropertyForPageProcessing
		property = identifier
	}
	dimension2 = FLUIDTEMPLATE
	dimension2 {
		file = EXT:bolius_boliusdk/Resources/Private/Templates/Helpers/Trompet.html
		variables {
			doktype = TEXT
			doktype.data = page:doktype
			identifier = USER
			identifier {
				userFunc = Bolius\BoliusProducts\Service\ProductService->getProductPropertyForPageProcessing
				property = identifier
			}
		}
	}
}
```