Include post balance information for rewards (#12598)

* Include post balance information for rewards

* Add post-balance to stored Reward struct

* Handle extended Reward in bigtable

Co-authored-by: Michael Vines <mvines@gmail.com>

storage-bigtable/proto/solana.bigtable.confirmed_block.rs

@@ -87,6 +87,8 @@ pub struct Reward {
     pub pubkey: std::string::String,
     #[prost(int64, tag = "2")]
     pub lamports: i64,
+    #[prost(uint64, tag = "3")]
+    pub post_balance: u64,
 }
 #[derive(Clone, PartialEq, ::prost::Message)]
 pub struct UnixTimestamp {