feat: add examples of multiple coins for command-line interfaces

[jaybxyz]

Summary

This issue requests to improve command-line interfaces by updating descriptions to have more contexts and providing more examples to make better developer-friendly environment. For example, NewUnstakeCmd accepts sdk.Coins type, and it only provides an example of a single coin. Developers who first read the description and the example won't know if it accepts multiple coins. It will be better to have an example of how to use multiple coins for the developers.

Proposal

We should add more examples on certain command-line interfaces to provide developer-friendly environment. Devs who first get to know about the farming module and play with it will be better off to know how to use each command if they have solid descriptions and more examples.

Tasks

• Add NewUnstakeCmd() multiple coins example and add test case for it
• Add NewStakeCmd() multiple coins example and add test case for it
• Add NewHarvestCmd() more examples and add test cases for it
• Add more description on NewAdvanceEpochCmd()
• Update the link in the description to point to the correct location

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For Admin Use

• Not duplicate issue
• Appropriate labels applied
• Appropriate contributors tagged
• Contributor assigned/self-assigned