Implement an operations manager

[sgreenbury]

The process for constructing operations involves creating JSON files and sending them with POST requests to the ION server. Currently these are managed manually.

Similar to the KeyManager, an OperationManager trait would be of benefit.

For example:

trait OperationManager {
    /// Saves operation to operation store.
    fn save(&self, op: Operation, operation_type: OperationType) -> Result<(), OperationManagerError>;
    /// Reads operation from operation store.
    fn read(&self, operation_type: OperationType) -> Result<Operation, OperationManagerError>;
    /// Sends operation to ION server.
    fn publish(&self, operation_type: OperationType) -> Result<(), OperationManagerError>;
    /// Restores operation from backup.
    fn restore(&self, operation_type: OperationType) -> Result<(), OperationManagerError>;
}

enum OperationType {
    Create,
    Update,
    Deactivate,
    Recovery,
    Attest,
}

impl OperationManager for IONController { }

The identification of operations should be aligned with unique identifiers used for storage in ION's mongodb so that quick lookups can be performed to confirm publication events and also provide a unique index.

Two related issues are #14 and #33.

[thobson88]

Related task: https://github.com/alan-turing-institute/trustworthy-id/issues/573#issuecomment-1677398882