Become storage provider workflow

[jfinkhaeuser]

• Use CLI to become storage provider
• Provide key, command to perform the on-chain workflow for this.

The full workflow should be more like this:

• generate new key pair/account on the storage node OR use existing key
• check if the chain already considers the key to belong to the storage role. If yes, just run.
  Otherwise:
• create a request to join a role specifying the public key, a member ID for the member that wants to join, and the role.
• (runtime/app) transfer balance to the new key
• (runtime/app) accept request as the referenced member
• wait for an event that states that the request has been accepted.

[jfinkhaeuser]

That checklist isn't really accurate any longer.

• Signup as a storage provider is done.
• Using the storage provider key in the node is WIP.