App hardening and debug optimizations

[bandogora]

• Added most config settings to prj.conf recommended by west build -t hardenconfig
• Replace stack sentinel with MPU and hardware stack protection on circuitdojo nrf9160 board
• Use arm-zephyr-eabi instead of arm-none-eabi for Cortex debug
• Remove CMake configurations from .vscode settings
• Set compiler optimizations for speed instead of size (-O2 instead of -Os)
• Add #ifdef CONFIG_BOOTLOADER_MCUBOOT guards throughout code to make disabling MCUboot easier (Cortex debugging doesn't work with MCUboot enabled)
• Decreased main stack size because there was no reason for it to be so large