* Migrate HPA v1 to v2beta2 HPA v2beta2 is defined and supported from 1.19+ onwards. Also HPA v2 is stable from 1.23 onwards. As we support 1.19+ onwards using HPA v2beta2. This change is base for custom metrics support we want to add later by modifying Function spec. * Add unit tests for hpa operations * Use constants instead of strings Signed-off-by: Sanket Sudake <sanketsudake@gmail.com>