add_multiply and multiply_add workflows

[giovannipizzi]

We still have both in the code, they are slightly different (one uses calcfunctions, the other a workflow with calcjobs and calcfunctions inside). Is this the main difference between the two? Where are these used (tutorials, test, ...)? Maybe it's a bit confusing to have very similar ones with different implementation, just swapping the names... We should probably replace one of the two with a slightly different task to avoid confusion?

@mbercx @sphuber @chrisjsewell @ramirezfranciscof