Slasher is missing --config-file option

[xrow]

🚀 Feature Request

Description

When running slasher --config-file=/etc/prysm/slasher.yaml you get and error.
For consistency I would like to see all programms to have the same config-file flag available.

Describe the solution you'd like

the slasher shall have the same option as the validator and the beacon-chain

Describe alternatives you've considered

It is of course also fine toconfgure the slasher without a config file.