Added governance KIP-71 fields

[jimni1222]

Proposed changes

This PR introduces adding KIP-71 governance fields with caver.rpc.governance APIs

Types of changes

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• Bugfix
• New feature or enhancement
• Others

Checklist

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• I have read the CONTRIBUTING GUIDELINES doc
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• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
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• Any dependent changes have been merged and published in downstream modules

Related issues

related to #662

Further comments

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