chore: add python 3.10 classifier

[anukaal]

added support for python 3.10

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Fixes #<issue_number_goes_here> 🦕

[parthea]

The python 3.10 is failing because the latest stable release of tensorflow 2.7.0 doesn't support python 3.10.
A pre-release version that supports python 3.10 is available: https://pypi.org/project/tensorflow/2.8.0rc0/ . Perhaps we should wait for a stable version.

nox > Running session unit-3.10
nox > Creating virtual environment (virtualenv) using python3.10 in .nox/unit-3-10
nox > python -m pip install mock asyncmock pytest pytest-cov pytest-asyncio -c /tmpfs/src/github/python-aiplatform/testing/constraints-3.10.txt
nox > python -m pip install -e '.[testing]' -c /tmpfs/src/github/python-aiplatform/testing/constraints-3.10.txt
nox > Command python -m pip install -e '.[testing]' -c /tmpfs/src/github/python-aiplatform/testing/constraints-3.10.txt failed with exit code 1:
Obtaining file:///tmpfs/src/github/python-aiplatform
  Preparing metadata (setup.py): started
  Preparing metadata (setup.py): finished with status 'done'
Collecting google-api-core[grpc]<3.0.0dev,>=1.26.0
  Using cached google_api_core-2.4.0-py2.py3-none-any.whl (111 kB)
Collecting proto-plus>=1.10.1
  Using cached proto_plus-1.19.8-py3-none-any.whl (45 kB)
Requirement already satisfied: packaging>=14.3 in ./.nox/unit-3-10/lib/python3.10/site-packages (from google-cloud-aiplatform==1.9.0) (21.3)
Collecting google-cloud-storage<2.0.0dev,>=1.32.0
  Using cached google_cloud_storage-1.44.0-py2.py3-none-any.whl (106 kB)
Collecting google-cloud-bigquery<3.0.0dev,>=1.15.0
  Using cached google_cloud_bigquery-2.32.0-py2.py3-none-any.whl (205 kB)
Collecting lit-nlp>=0.4.0
  Using cached lit_nlp-0.4.1-py3-none-any.whl (746 kB)
ERROR: Could not find a version that satisfies the requirement tensorflow>=2.3.0 (from google-cloud-aiplatform[testing]) (from versions: 2.8.0rc0)
ERROR: No matching distribution found for tensorflow>=2.3.0

[parthea]

FYI @vinnysenthil

[sasha-gitg]

Closing in favor of #1644