When submitting a new result, Profile is currently mandatory and it's not explained what it is.

Let's make it optional.

Also, let's add some grayed text explanation into the field (just like we do with Bug URLs), e.g.:
> Optional details about your system (hardware specs, software configuration, etc) relevant for the current test day

Let's display this info text only when Profile is not overridden by the `! ProfileText` command in metadata definition (alternatively, we could extend the spec to also provide the explanation comment in the metadata).