Refactor: rename Role.Spec.Replicas to some other

[vasiliy-t]

Problem statement

Replicas denotes number of equal entities but Role.Spec.Replicas specifies number of different entities - number of shards within Role. This results in confusing expectations when scaling role's

Possible solution

Rename .spec.replicas to size

Names must be predictable. e.g. replicas means number of equal things, number, size, quantity means everything and nothing.