Secrets manager introduced to commands

[Nemanja0x]

Description

Commands stake, unstake, withdraw, validator info use secret manager to provide access to cloud secret storage or local disc.
Naming of the flags are standardized for all commands:
DataPathFlag = "data-dir" - for local storage
ConfigFlag = "config" - cloud config

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)

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

Manual tests

[Stefan-Ethernal]

Generally looks good.

Points to consider addressing:

• What should we do with command/rootchain/emit/emit.go and command/rootchain/initcontracts/init_contracts.go? Those two commands are expecting hex-encoded private key to be provided via the CLI flag, but not sure if is it ok to leave it like that.
• Also just mark DataPathFlag and ConfigFlag mutually exclusive in each command it accommodates it.

[vcastellm]

Late review but shared flags between subcommands can be defined in the top level command if I'm not wrong.