Tag-specific FD parameters

[abhisrkckl]

Since different instruments may be using different templates, we may need multiple FD parameters for different telescopes, backends etc.

One way to implement this will be as a PrefixMaskParameter which has properties of both prefix and mask parameters.

[rossjjennings]

As discussed at the PINT meeting today, a similar, but not necessarily directly related, issue is #1059 (Mask parameters have unhelpful names).