build: Add envoy_extension_py_test for excluding extensions with py_tests

[markguan-stripe]

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Commit Message: Add envoy_extension_py_test too allow for excluding extensions that have py_tests in builds
Additional Description:

Currently, we can't exclude the envoy.filters.network.kafka_broker extension from our build because the kafka_broker_integration_test py_test will fail. This prevents us from reducing our build size. Instead, we should add a wrapper around py_tests used in extensions, similar to envoy_extension_cc_test, so that the test won't be included as a target when extension_name is not in EXTENSIONS. This will be useful going forward if more extensions end up using py_tests.

Risk Level: Low
Testing: Manual testing on all tests
Docs Changes: N/A
Release Notes: N/A
Platform Specific Features: N/A
[Optional Runtime guard:]
[Optional Fixes #Issue]
[Optional Deprecated:]
[Optional API Considerations:]

[repokitteh-read-only]

Hi @markguan-stripe, welcome and thank you for your contribution.

We will try to review your Pull Request as quickly as possible.

In the meantime, please take a look at the contribution guidelines if you have not done so already.

🐱

Caused by: #15319 was opened by markguan-stripe.

see: more, trace.

[murray-stripe]

/retest

[repokitteh-read-only]

Retrying Azure Pipelines:
Retried failed jobs in: envoy-presubmit

🐱

Caused by: a #15319 (comment) was created by @murray-stripe.

see: more, trace.

[markguan-stripe]

/retest

[repokitteh-read-only]

Retrying Azure Pipelines:
Retried failed jobs in: envoy-presubmit

🐱

Caused by: a #15319 (comment) was created by @markguan-stripe.

see: more, trace.