Improve eip712 compatibility

[ramacarlucho]

Closes: #1245 #1247

Description

The current implementation for eip712 only supports amino encoded msgs. This changes aim to detect the current encoding of the msg and the inner structures and create the eip712 types accordingly.

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• Wrote unit and integration tests
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• Added relevant godoc comments.
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
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