Handle collisions in transactions table

[telezhnaya]

This PR will hopefully close #84 in one day

[telezhnaya]

I want to save the reference here https://github.com/near/near-indexer-for-explorer/blob/master/src/db_adapters/transactions.rs#L53-L57

let transaction_hash_suffix = "_issue84_".to_owned() + &block_height.to_string();