containerapp : allow creating a new revision both with a target label (preview) and a base revision

**Related commands**

`az containerapp update` and `az containerapp revision copy`

**Is your feature request related to a problem? Please describe.**

When using the `Deployment labels (preview)` revision mode, we want, for each label, to use the latest revision of the label as the "base" for the new revision.

We can set `--from-revision` using `az containerapp revision copy`, but we can't set `--target-label`.
We can set `--target-label` using `az containerapp update`, but we can't set `--from-revision`.

The default behavior of ACA if I'm not mistaken is to use the latest created revision both for the target label but also for the revision to copy from.

So, it seems that we can't have labels with their own "lifecycle", where each revision is created from the previous one with the same label, using az cli.

**Describe the solution you'd like**

Ideally, we should:
- Be able to set `--from-revision` with `az containerapp update`
- And be able to set `--target-label` with `az containerapp revision copy`

Or any other solution that allows us to have labels that are considered kind of "silos".

**Describe alternatives you've considered**
Listed above