lib(babe): Gossamer should use current system timestamp at babe

[EclesioMeloJunior]

Issue summary

• Currently, Gossamer babe was updated to solve the runtime error Timestamp must match 'CurrentSlot' which is caused by a problem while setting the timestamp value in the inherent data, however, the fix uses a pre-calculated timestamp which is not the right approach. We should use the current system time as the timestamp value in the inherent data

Other information and links

• Substrate deals with by delaying (sleeping) instead of a timer https://github.com/paritytech/substrate/blob/fbddfbd76c60c6fda0024e8a44e82ad776033e4b/client/consensus/slots/src/slots.rs#L125