[Doc] Improve Python client apidoc with pydoctor tool

[tisonkun]

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• I searched in the issues and found nothing similar.

What issue do you find in Pulsar docs?

This should be done with apache/pulsar-client-python#28. But we still need to update the pulsar-site apidoc generate process. Open an issue for tracking.

What is your suggestion?

Not applicable.

Any reference?

No response

Are you willing to submit a PR?

• I'm willing to submit a PR!