Add stake flag to manifest command

[Stefan-Ethernal]

Description

This PR introduces stake flag to the manifest command. This flag enables specifying genesis validators' stake. Prior to this PR, validators' balances were used as stake amount staked.

If a stake flag is not provided, then the stake defaults to 1M tokens (the same as with the pre-mine balance).

Changes include

• Bugfix (non-breaking change that solves an issue)
• Hotfix (change that solves an urgent issue, and requires immediate attention)
• New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)

Breaking changes

Introduced stake field as part of InitialValidatorSet in the genesis specification.

Checklist

• I have assigned this PR to myself
• I have added at least 1 reviewer
• I have added the relevant labels
• I have updated the official documentation
• I have added sufficient documentation in code

Testing

• I have tested this code with the official test suite
• I have tested this code manually

[codecov]

Codecov Report

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The diff coverage is n/a.

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[vcastellm]

🎩

[Nemanja0x]

1. I would like stake to be a mandatory field for each validator (maybe to require to be greater than zero)
2. Open question is if the stake flag is independent from balance flag. If it is, then the total amount of tokens that a genesis validator owns is stake + balance.

These are requirement questions and it would be good to discuss them before merging this PR.