Improve ActionStatus docs

[SijmenHuizenga]

In the docs, the possible actionStatus values describe RETRIEVED:

Device has retrieved the artifact.

I interpret this as:

The device has downloaded the artifact.

In DmfActionStatus.java, we learn that RETRIEVED means:

Action has been send to the target.

Which I interpret as

The instruction to download the artifact as been received by the target.

~From some initial experimentation it seems the latter interpretation is correct, but I'm not entirely sure.~ I'm not sure what the right interpretation is. Can we update these docs to be more specific?

If it turns out I'm blind and this is explained somewhere else in the docs in more details, would we be able to link to those docs in this table?

[lizziemac]

@SijmenHuizenga where in the docs did you find it explained? it looks like this is still vague in the DMF documentation