Initialize next_idx in Raft::new

[Fullstop000]

In Raft::new, we always create a ProgressSet with setting next_idx 1 in each Progress:

raft-rs/src/raft.rs

Lines 251 to 255 in f7f7d01

	for p in voters {
	let pr = Progress::new(1, r.max_inflight);
	if let Err(e) = r.mut_prs().insert_voter(*p, pr) {
	fatal!(r.logger, "{}", e);
	}

In the situation where recovering the raft node, I think maybe we can just use the current Snapshot's meta index as same as the implementation in restore_raft :

raft-rs/src/raft.rs

Lines 1984 to 1987 in f7f7d01

	let mut prs = self.prs.take().unwrap();
	let next_idx = self.raft_log.last_index() + 1;
	prs.restore_snapmeta(meta, next_idx, self.max_inflight);
	prs.get_mut(self.id).unwrap().matched = next_idx - 1;

[hicqu]

When a peer becomes leader, it will reset next_idx to last_index + 1 for all followers. So I think it's OK?

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I just want to make the implementation stay consistent with resotre_snapmeta :). Feel free to close this.