feat: add --wait flag to upgrade-service

[blgm]

Does this PR modify CLI v6, CLI v7, or CLI v8?

This PR is aimed for vNext (v9), but could be cherry-picked to v8 if that was considered appropriate.

Description of the Change

Most of the service commands (e.g. "cf update-service") take a --wait flag to wait for completion. For some reason "cf upgrade-service" did not, and this commit resolves that inconsistency.

Why Is This PR Valuable?

It makes the service commands more usable and more consistent

Why Should This Be In Core?

It's a modification to a core command

Applicable Issues

None

How Urgent Is The Change?

Not urgent at all

Other Relevant Parties

Who else is affected by the change?

No-one