Build service update patch bodies (#492)

> [!NOTE]
> This is a no-op in the sense that no commands call the new code!

Implemented `BuildUpdateRequest`.

It takes in:
- The current state of the Service
- The updates supplied via the CLI

It returns:
A PATCH body to send to the PATCH /service endpoint.

GROW-2375

GitOrigin-RevId: 26cde570ab72b7980c483e93fba5ca1dfe7fb1ad

Author: davidharting