Generate zome call signing keys on client side, based on user-input password

AC:
- add function to holochain-runtime: authorize_signing_key(installed_app_id: String, public_key: Vec)
- calls grant_zome_call_capability for the specified public key and app id
- authorize_signing_key passed up through ffi crate and HolochainService bindings
- HolochainServiceClient function signZomeCall will:
- check if signing private key is stored to app storage
- if not
- generate one based on random password
- call authorize_signing_key
- sign the zome call with the private key
- return the signed zome call
- add another HolochainServiceClient function signZomeCallWithPassword:
- generate signing key based on password input
- sign the zome call with the private key
- return the signed zome call
- modify tauri-plugin-holochain-service-client:
- config specifies if zome calls are signed with auto-generated key or password

Also consider including a UI view that is displayed above the app to enter a password for calling signZomeCallWithPassword

See example implementation:
- https://github.com/ThetaSinner/ekto/blob/main/ekto-lib/src/index.ts#L87
- https://github.com/ThetaSinner/ekto/blob/main/src/approve_key.rs