[1.0-beta3 -> main] clear state history's finality log if savanna transition is forked out

[spoonincode]

main merge of #301:

Avoid state history finality log failure and node shutdown if savanna transition is forked out. Resolves #289. This is a fairly simple change that erases all finality data log files and reopens a fresh head log when savanna finality data is removed (which can only happen upon the transition being forked out).

An even simpler alternative would be to always write the std::optional<finality_data_t> out, which we could do instead, but that puts a little more burden on consumers.

[ericpassmore]

Note:start
group: STABILITY
category: INTERNALS
summary: Clear out the state history log when Savanna transition is forked out.
Note:end