Hide yearly billing toggle if there are no yearly billing deets to show

[knolleary]

Alternative fix for #8218 - replaces #8221

Rather than rip out the toggle, this fixes up the conditional logic for whether it is shown or not. They already had a v-if conditional on, but the value wasn't being set consistently.

I have also updated the code that mapped a blank pricing detail to display 'free' so that it no longer does that. We don't have a free tier - and it only saved having to type the word 'free' into the pricing description box.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.20%. Comparing base (fad6271) to head (8b33f4b).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #8232   +/-   ##
=======================================
  Coverage   76.20%   76.20%           
=======================================
  Files         443      443           
  Lines       23728    23728           
  Branches     6315     6315           
=======================================
  Hits        18081    18081           
  Misses       5647     5647           

Flag	Coverage Δ
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