FederatedOperation field payload exposed to modifications.

[GCHQDev404]

Describe the bug
FederatedOperation now exposes internal field payload which can now be externally modified via getOperations() unlike the getPayload() operation

Expected behaviour
payload should not be able to be externally modified.

Additional context
since #3077
see

Gaffer/store-implementation/federated-store/src/main/java/uk/gov/gchq/gaffer/federatedstore/operation/FederatedOperation.java

Lines 166 to 168 in 4a43704

	public Operation getPayloadOperation() {
	return hasPayloadOperation() ? payloadOperation.shallowClone() : null;
	}

[t92549]

Good catch, I missed this! Can probably be done as part of #3078