Shell Manager - Execute and run gadgets

[shekohex]

After downloading the blueprint #158 it should be ready to be executed, each blueprint would expect to be executed with a set of env variables that are set by the manager for the child process (or remote process):

1. RPC_URL: The remote RPC url for tangle
2. KEYSTORE_URI: the keystore file where the keys are stored and could be retrieved.
3. DATA_DIR: is an isolated path for where this gadget should store its data (database, secrets, …etc)
4. BLUEPRINT_ID: the active blueprint ID for this gadget
5. SERVICE_ID: the active service ID for this gadget
6. HEALTHCHECK: If set, the gadget just prints its version and exist with a status code zero, to check if the binary is configured correctly.

Once it starts, the child process or the remote process should be kept alive, and monitored by the shell manager. If it fails or panicked, the shell manager should report the issue to the operator and depends on the configuration, the gadget may need to be restarted again.

[shekohex]

For keystore URI: :mem:, or file://... and kms://...