Specify a standard for `metadata` for chain

[lumtis]

Determine a standard for the metadata format of a chain.

metadata represents generic bytes but the Ignite CLI and Launchpad will consider a standardized JSON format for their usage

The metadata must allow:

• Specify the version of Ignite CLI used to generate the genesis from Ignite information
• Specify the source URL and Hash to get information to show about a chain on the launchpad

We should write down this standard somewhere in docs

[lumtis]

Defined in the scr