Add consistent slowly changing side inputs support

[damccorm]

Add implementation for slowly changing dimentions based on [design doc](https://docs.google.com/document/d/1LDY_CtsOJ8Y_zNv1QtkP6AGFrtzkj1q5EW_gSChOIvg/edit]

Imported from Jira BEAM-9650. Original Jira may contain additional context.
Reported by: Ardagan.