docs: add consumer onboarding documentation

[MSalopek]

Summary

Add a documentation page outlining how validators should onboard onto consumer chains.

Problem Definition

At present, we do not provide any guidelines as to how to join consumer chains.

Proposal

Write and publish docs outlining the consumer onboarding procedure and use it aliongside the consumer onboarding checklist.

Use resources from previous and current testnets to come up with clear steps and considerations:

Launch process:

• https://github.com/hyphacoop/ics-testnets/blob/main/docs/Consumer-Chain-Start-Process.md
• https://github.com/hyphacoop/testnets/blob/master/replicated-security/CONSUMER_LAUNCH_GUIDE.md

Game of chains

• https://github.com/hyphacoop/ics-testnets/tree/main/game-of-chains-2022

Persistent testnets:

• https://github.com/hyphacoop/testnets/tree/master/public
• https://github.com/hyphacoop/testnets/tree/master/replicated-security

Linked to: #750

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For Admin Use

• Not duplicate issue
• Appropriate labels applied
• Appropriate contributors tagged
• Contributor assigned/self-assigned
• Is a spike necessary to map out how the issue should be approached?

[MSalopek]

Added in PR

Docs:

• Onboarding Checklist
• How to join