Autogenerate Regional Mask Input Stream

[q-rai]

A couple of analysis members now have region mask capabilities now. The region masks used are included using an input stream. So far, everyone has been manually copying the following snippet into their streams.ocean, but it would be much more convenient if this could be auto generated.

<stream name="regionalMasksInput"
        type="input"
        mode="forward;analysis"
        filename_template="masks.nc"
        input_interval="initial_only"
        runtime_format="single_file">
        <var_struct name="regions"/>
</stream>

[q-rai]

I don't expect to have time to do this myself before I leave, so this is totally up for grabs for anyone who knows how to do it!

@milenaveneziani would definitely appreciate this change!

[milenaveneziani]

I may be wrong, but I think this belongs to the main Registry.