feat(espcoredump): Allow writing to both flash and UART (IDFGH-12554)

[nebkat]

Writing core dump to UART is useful when actively developing in esp monitor and you want to immediately check the output.
Writing to flash is separately useful when a crash might occur when esp monitor is not connected and you want to inspect the crash later.

This PR allows both options to be enabled at the same time.

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[erhankur]

@nebkat Thank you for your contribution. We will evaluate internally and decide whether to use both options at the same time.