feat: add MMU commands to autoUppercaseBlacklist

[zaventh]

M707, M708 are related to Prusa MMU devices and require passing a hexadecimal argument with a lower-cased address.

More information: https://reprap.org/wiki/G-code#M707:_Read_from_MMU_register

Resolves #4864

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What does this PR do and why is it necessary?

Allows sending relevant MMU gcode commands without having to manually blacklist them