Add deprecation warnings to GCE provisioner (#5506)

[annagiroti]

When using the GCE provisioner, Toil will now emit deprecation warnings in gceProvisioner.py, common.py, and cwltoil.py to notify users that the GCE provisioner will be removed in a future release. Users should migrate to Kubernetes-based autoscaling.

Resolves #5506

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[adamnovak]

I figured this might result in multiple warnings in a single run, and I checked, and when I run a CWL workflow with the GCE provisioner I indeed see all three of these warnings in one run, with increasing levels of the logging system having been set up properly at each point.

(venv) [anovak@swords toil]% toil-cwl-runner --provisioner=gce '#workflow/github.com/denis-yuen/dockstore-whalesay:0.10'
The GCE provisioner is deprecated and will be removed in a future release. Please use Kubernetes-based autoscaling instead.
/Users/anovak/workspace/toil/venv/lib/python3.10/site-packages/google/api_core/_python_version_support.py:273: FutureWarning: You are using a Python version (3.10.18) which Google will stop supporting in new releases of google.api_core once it reaches its end of life (2026-10-04). Please upgrade to the latest Python version, or at least Python 3.11, to continue receiving updates for google.api_core past that date.
  warnings.warn(message, FutureWarning)
Toil's GCE provisioner is deprecated and will be removed in a future release. Please use Kubernetes-based autoscaling instead.
Pulling debian:8 with docker...
INFO:cwl_utils.image_puller:Pulling debian:8 with docker...
Image successfully pulled: debian:8
INFO:cwl_utils.image_puller:Image successfully pulled: debian:8
...
[2026-05-12T17:09:35-0400] [MainThread] [W] [toil.common] Toil's GCE provisioner is deprecated and will be removed in a future release. Please use Kubernetes-based autoscaling instead.
...

The warning looks the nicest (and is most noticeable, because it gets the logging colors) at the final point, which is the one that comes from common.py. I would remove the other copies of the warning and just issue it in that one place.

Is there a good reason I don't know about that explains why we'd need it in all 3 of these places?