v1.2.1 to increase default SPI_CLOCK_MHZ clock to 20MHz from 8MHz and to Update examples to use DHCP with built-in ESP32 Ethernet MAC Address

[khoih-prog]

Releases v1.2.1

1. Increase default SPI_CLOCK_MHZ clock to 20MHz from 8MHz
2. Update examples to use DHCP with built-in ESP32 Ethernet MAC Address

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This discussion was created from the release v1.2.1 to increase default `SPI_CLOCK_MHZ` clock to 20MHz from 8MHz and to Update examples to use `DHCP` with `built-in ESP32 Ethernet MAC Address`.