golioth: add golioth_req_rsp_default_handler() default response handler

[mniestroj]

Replace static default_req_cb() with a golioth_req_rsp_default_handler() that produces error/debug messages on received response. Especially error messages are useful in case of CoAP ACK timeout or non-2 (non-success) CoAP response code class.

Add additional "hidden" (not documented to SDK consumers) functionality about logging additional module/component information string, so that it is easier to locate source component from specific log comes from. As an example for settings.c this is what will appear in Zephyr console:

  <dbg> golioth: Settings response ACK
                 73 65 74 74 69 6e 67 73  20 73 79 6e 63 65 64  |settings  synced

as a result of successful acknowledgment, when debug logs are enabled.

Make this function private to SDK internal implementation, so that above experimental "component infrmation" logging won't be used by SDK consumers.

[github-actions[bot]]

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