Make a private function for sendTx

[colin-axner]

Summary

Add a private function sendTx which acts in a similar fashion to registerInterchainAccount, it should handle the shared legacy/new functionality and the calling functions (either legacy or message server) should do their own differentiating logic within their respective functions

For example, the legacy API should pass the absolute timestamp where the message server should pass the calculated absolute timestamp (current block time + relative timestamp)

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