raft follower should add the judgment of leader lease valid when process askvote to prevent split brain

[tangyuanzhang]

Current code that process voting election requests may cause split brain (ep: network issue)，I think it would be better to add some judgment

[critical27]

Would you name one split brain case? What you implemented above is called leader stickness, which is generally used in raft, but whether check leader stickness does not impact leader election.

[tangyuanzhang]

A(leader， lease 30s) ，B ,（follower） C （follower）, C restart（isBlindFollower, quick election）， send askvote reques to A（lost）, send askvote request to B，B votes for C，now A is leader， C is leader；

[tangyuanzhang]

A(leader， lease 30s) ，B ,（follower） C （follower）, A rocksdb manual compaction, write stall, sendheart only step2(not send log), A and C network isolation，C can't receive heartbeat， send askvote request to B，B votes for C，now A is leader， C is leader；

[tangyuanzhang]

The judgment of role and pre_vote can be removed

[critical27]

Same as #5352, close it.