Add PATCH schemas to arm-common-types

A few common-types schemas will not work in PATCH bodies, due to having required properties or using the wrong visibility.
- Ensure that PATCH schemas are generated for necessary arm-common-types types as part of common-types swagger generation
- Ensure that PATCH requests use the new common-types schemas

This should be required for:

ManagedServiceIdentity
SystemAssignedServiceIdentity
Plan
Sku
TrackedResource

Locate the common-types Swagger generation and PATCH request schema generation entry points, then inspect how ManagedServiceIdentity, SystemAssignedServiceIdentity, Plan, Sku, and TrackedResource are handled. Done means the necessary PATCH schemas are generated and PATCH requests use those common-types schemas.

Written by the indexing model from the issue text.