[REFACTOR] Make WorkflowState more easily updated with a Builder Constructor from a previous state

[dbwiddis]

Is your feature request related to a problem?

Making one change on a WorkflowState object requires re-adding all the individual fields through the builder. See for example:

flow-framework/src/main/java/org/opensearch/flowframework/transport/GetWorkflowStateResponse.java

Lines 51 to 55 in e3a8784

	this.workflowState = new WorkflowState.Builder().workflowId(workflowState.getWorkflowId())
	.error(workflowState.getError())
	.state(workflowState.getState())
	.resourcesCreated(workflowState.resourcesCreated())
	.build();

What solution would you like?

Create a constructor on the Builder that accepts a previous state as its input and copies over the fields. Then only the changed fields need to be added. We do this for the Template class here.

What alternatives have you considered?

Leaving it as-is.

Do you have any additional context?

I actually did the work for this in my POC PR #631 so someone just needs to copy-paste some of those changes. :-)