RPC: Change timeout to `time.duration` on `traceTx`

[crypto-facs]

Currently TraceConfig type on protobuf has Timeout as string and is later parse inside of the function. This Timeout parameter should be of type time.duration to avoid having this extra step.

This was done in the first place to comply with Go-Ethereum debug_traceTransaction grpc endpoint.

[iverc]

@crypto-facs Addressed, PTAL #594.

[tomtau]

https://github.com/tharsis/ethermint/pull/594#issuecomment-928820789 @crypto-facs is there an issue on Go Ethereum for this?

[github-actions[bot]]

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