[Design Doc] On Chain Messages

[wilwade]

Might need to reference #7

Blocked By https://github.com/Liberty30/polkadot-experiments/issues/53

Notes:

• Starting with the gas version of this that can be converted to capacity later
• On chain messages should have some required schema
• Someway to do extended custom schema
• Message Schemas should be able to be created, but not modified? Perhaps versioned?
• Could schemas have validation rules?
• Must be validated as FROM a specific static id