Missing dependency on protobuf

[sorindumitru]

When trying to use the spiffe package in a venv I got this error:

>>> from spiffe import JwtSource
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/sdumitru/github/spiffe/venv/lib/python3.12/site-packages/spiffe/__init__.py", line 2, in <module>
    from .workloadapi.x509_source import X509Source  # noqa: F401
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/sdumitru/github/spiffe/venv/lib/python3.12/site-packages/spiffe/workloadapi/x509_source.py", line 25, in <module>
    from spiffe.workloadapi.workload_api_client import WorkloadApiClient
  File "/Users/sdumitru/github/spiffe/venv/lib/python3.12/site-packages/spiffe/workloadapi/workload_api_client.py", line 31, in <module>
    from spiffe.proto import (
  File "/Users/sdumitru/github/spiffe/venv/lib/python3.12/site-packages/spiffe/proto/workload_pb2.py", line 6, in <module>
    from google.protobuf import descriptor as _descriptor
ModuleNotFoundError: No module named 'google'

After installing the protobuf package in the venv, I was able to use the package.

I only tested the spiffe package, i don't know if the spiffe-tls package has the same issue or not.