[NV24] F3 activation epoch

[LesnyRumcajs]

Post NV24 (~2 weeks) after the NV24 upgrade on mainnet, F3 is supposed to be activated. It's not yet clear what the solution will look like. Likely hard-coding the epoch (with some environmental variables) will be the solution both in Lotus and Forest. The issue is that the initial power table needs to be stored somewhere and we cannot read past 2000 epochs.

• F3 activation epoch is set (and configurable via an environmental variable),
• There's an option to opt-out from F3 if need be (currently it's opt-in, we may need to inverse that logic).

[LesnyRumcajs]

@hanabi1224 Could you please coordinate with the FilOz team on this? I believe there will be some testing on Butterflynet next week. Also, we tentatively scheduled F3 activation to 1 day after the calibnet upgrade.

[LesnyRumcajs]

See filecoin-project/lotus#12552

[hanabi1224]

Will do.

[LesnyRumcajs]

Determine the number for calibnet and mainnet.