Propagate SSL settings to curl's SSL context

[lpsinger]

• Fixes #3751.
• Fixes confluentinc/confluent-kafka-python#1702.
• Fixes confluentinc/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 (https://github.com/nasa-gcn/gcn-kafka-python/issues/49) by using librdkafka's builtin OIDC token refresh callback (https://github.com/nasa-gcn/gcn-kafka-python/pull/22).