Add Trident Mellow Flyf407zg in SPI mode; This PR will not work properly without PR #257

[GadgetAngel]

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*Add Trident Mellow Flyf407zg in SPI mode, This PR will not work properly without PR #257 . It contains a link to the information in PR #257

*In Community/Electronics/ added the following:

1. GadgetAngel folder
2. images subfolder

*updated Index.md file in Community/Electronics/ to add "Trident - Mellow FLYF407ZG Wiring for both SPI and UART modes" (tri_flyf407zg_wiring.md) *tri_flyf407zg_wiring.md is a parent to tri_flyf407zg_spi_wiring.md

*reused three additional files: a. flyf407zg_additional_resources.md b. flyf407zg_RaspberryPi.md c. flyf407zg_Resources.md

*added initial Removal of Jumpers diagram *added initial preparation - Set Jumpers diagram for Mellow Flyf407zg in SPI mode *Added description for Trident wiring diagram in Mellow Flyf407zg in SPI mode *added the heatsink diagram to remind user to ensure that the heatsinks are installed on the stepper motor drivers for: *Added the following MCU with heat sinks in SPI mode *added URL to the Klipper Configuration by Antage(https://gist.githubusercontent.com/antage/1976d9df8e8a1126ebbe6f3935145394/raw/6bc4c53194be75a9889fba754ffa61fbb5c7cb89/printer.ini) for Mellow Flyf407zg *informed use that the above config file needs to be changed from UART to SPI *added links to other resources