feat: iap upgrade and downgrade (#110)

[FlorianKe]

Backport #110

[codecov-commenter]

Codecov Report

❌ Patch coverage is 36.20690% with 37 lines in your changes missing coverage. Please review.
✅ Project coverage is 66.93%. Comparing base (932f5ab) to head (439d20d).

Files with missing lines	Patch %	Lines
...app-purchase-checkout-subscription-change/index.ts	0.00%	13 Missing ⚠️
src/Services/StoreClient.php	0.00%	12 Missing ⚠️
...nent/sw-in-app-purchase-checkout-overview/index.ts	57.14%	3 Missing ⚠️
...ses/component/sw-in-app-purchase-checkout/index.ts	84.21%	3 Missing ⚠️
src/Controller/InAppPurchasesController.php	0.00%	2 Missing ⚠️
...nistration/src/module/sw-in-app-purchases/index.ts	0.00%	2 Missing ⚠️
src/Services/InAppPurchasesService.php	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##              6.6.x     #117      +/-   ##
============================================
- Coverage     68.63%   66.93%   -1.70%     
- Complexity       66       69       +3     
============================================
  Files            35       36       +1     
  Lines          1068     1107      +39     
  Branches        128      135       +7     
============================================
+ Hits            733      741       +8     
- Misses          306      337      +31     
  Partials         29       29              

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