[Python] Add ca_cert_data parameter

[micolous]

The ca_cert_data parameter lets a client validate a server's CA certificate chain using a variable/constant containing PEM (str) or DER (bytes) data, rather than needing to reference a file on disk.

Naming is based on what urllib3 calls this parameter.

I've applied a similar patch to some locally generated bindings for asyncio and urllib3, and it's working there.

@cbornet (2017/09) @tomplus (2018/10) @krjakbrjak (2023/02) @fa0311 (2023/10) @multani (2023/10)

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[micolous]

Now ready for review. I've tested this with asyncio as well now, that's working as I expect.

CI failures were due to me using some Python 3.10+ syntax (str | bytes instead of Union[str, bytes]).

[multani]

lgtm