Add support for CA bundles

[moritz89]

Instead of only a single CA cert, support CA bundles to verify the TLS connections.

https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/protocols/esp_crt_bundle.html

To add support, one option is to add a new constructor that accepts a pointer and then calls setCACertBundle on the WiFiClientSecure instance.

Espressif supports these bundles via an archive that reduces the required flash memory and only loads the CA indexes instead of the entire certificate into memory. The respective cert is then loaded on TLS connection setup.