Submit and handle equivocation report

[kishansagathiya]

Issue summary

• In case of an equivocation, substrate reports it (https://github.com/paritytech/substrate/blob/c24431eb6a95197550b30715a4c124be1aea79de/client/consensus/babe/src/lib.rs#L1228)
• by reporting, I mean, it submits an unsigned extrinsic containing equivocation proof and key ownership proof.
• On submitting this, an offence gets reported. (look for report_offence). I wonder if this method of reporting offence is peer scoring equivalent of substrate. More investigation is needed here.
• Interesting functions to look for in substrate are submit_report_equivocation_unsigned_extrinsic, submit_unsigned_equivocation_report, report_equivocation_unsigned, do_report_equivocation

At the moment we don't report equivocation. The task list here is

• We report the equivocation the way substrate does.
• Investigate what should we do on finding these reports and offence

Other information and links

• Inspired from Author a sibling block in case best block's slot is same as current slot  #2827 (comment)

[timwu20]

Pretty sure this is closed by #2827