Shifu should allow user to configure `/` instruction

[tomqin93]

Is your feature request related to a problem? Please describe.

Currently when a user tries to configure deviceShifu with / instruction, it conflicts with the embedded instructionNotFoundHandler which cannot be overwritten and throws an error.

Describe the solution you'd like

Allow user to configure / as an instruction

Describe alternatives you've considered

Use another forward proxy in front of Shifu

Additional context

[saiyan86]

@tomqin93 assign?