coap: Add mbedTLS and debug config for CoAP build option (IEC-19)

[ESP-YJM]

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Change description

1. Add COAP_MBEDTLS_SUPPORT Kconfig to make CoAP support DTLS or not. This can help save about 80 KB firmware size.
2. Depend on COAP_MBEDTLS_DEBUG Kconfig to make CoAP support debug or not. This can help save about 20 KB firmware size.

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[mahavirj]

This will also make the underlying transport insecure. I am not sure how this config would be really helpful, can you please elaborate?

[ESP-YJM]

When only need CoAP and no DTLS, we can disable this config and it will save a lot of firmware size. I agree that CoAP transported without DTLS is not secure, but users can encrypt the CoAP payload themselves and then transport it using CoAP, which is also a way to use it. Just as RainMaker uses HTTP for local control instead of HTTPS, the data content is encrypted by negotiation. And I am going to add CoAP transmission to the protocomm layer. At present, I am comparing the memory, time and firmware size of HTTP and CoAP. Later, I will provide MR internally, and I need you to share your suggestions.