Generate keys on startup

[gregdhill]

Is your feature request related to a problem? Please describe.
Vault setup is complicated due to the number of steps required. Operators may use the light-client instead of downloading Bitcoin core but we still require keys to be installed manually.

Describe the solution you'd like
If the Vault does not detect a key file on startup it should generate the Substrate (and Bitcoin) keys. It should wait until the account is funded if there is no faucet available, register those and then continue normal operation.

Describe alternatives you've considered
We should also consider other ways to package the Vault client to deploy it more easily in places such as AWS.

Additional context
The Vault client already includes separate commands to generate the keys:

interbtc-clients/vault/src/main.rs

Lines 34 to 37 in d8826bb

	/// Generate the WIF encoded Bitcoin private key.
	GenerateBitcoinKey(GenerateBitcoinKeyOpts),
	/// Generate the sr25519 parachain key pair.
	GenerateParachainKey(GenerateParachainKeyOpts),