[NT-1529] Add PLN Currency Selection

[justinswart]

📲 What

Adds the Polish Złoty (PLN) to our currency selection.

🤔 Why

Poland is a country that we will soon be rolling out currency support to.

🛠 How

• Added translations for the currency string.
• Updated our Currency type which makes the currency available for selection by way of its CaseIterable conformance.

👀 See

Before 🐛	After 🦋

✅ Acceptance criteria

• Navigate to your user settings, update your currency to PLN, this change should be persisted. Note: This work is still pending on the back-end and this PR is blocked for now.

[codecov]

Codecov Report

Merging #1298 into master will decrease coverage by 0.00%.
The diff coverage is 38.46%.

@@            Coverage Diff             @@
##           master    #1298      +/-   ##
==========================================
- Coverage   79.35%   79.35%   -0.01%     
==========================================
  Files        1109     1109              
  Lines      107066   107077      +11     
==========================================
+ Hits        84963    84966       +3     
- Misses      22103    22111       +8     

Impacted Files	Coverage Δ
Library/Strings.swift	20.69% <0.00%> (-0.02%)	⬇️
Library/Currency.swift	62.50% <50.00%> (-0.84%)	⬇️
...rary/ViewModels/SelectCurrencyViewModelTests.swift	100.00% <100.00%> (ø)

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[singhhari]

lgtm