Propagate SSL settings to curl's SSL context

[lpsinger]

• Fixes ssl.ca.location and related settings do not affect libcurl requests for OIDC token endpoints #3751.
• Fixes SSL cert problem "self-signed certificate" and ignored SSL options confluent-kafka-python#1702.
• Fixes Fails to obtain OAuth2 token using CA certificate on Ubuntu while it works on MacOS and Windows confluent-kafka-dotnet#2106.

Please note, I need some help to update the unit tests. Adding an rd_kafka_t * to the rdhttp functions means that the unit tests require at least a partly initialized rd_kafka_t struct.

Merging this will allow us to fix a very annoying error that our users are seeing (nasa-gcn/gcn-kafka-python#49) by using librdkafka's builtin OIDC token refresh callback (nasa-gcn/gcn-kafka-python#22).

[confluent-cla-assistant]

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