Add missing API source payment partial view for Stripe payment sources

[rainerdema]

Summary

Fixes #251

This PR resolves an issue where a missing partial for the Stripe payment source was causing an exception during the order API GET call in solidus_backend. The new payment view is added to render payment source data as JSON.

For more details in solidusio/solidus: https://github.com/solidusio/solidus/blob/e878076f2ed670d07654ab6293a16588743f2fa6/api/app/views/spree/api/orders/_big.json.jbuilder#L36-L43

Refer to this comment for more details about the mentioned exception: https://github.com/solidusio/solidus_stripe/issues/251#issuecomment-1485187657

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[codecov[bot]]

Codecov Report

Merging #270 (27f8eed) into master (105220e) will decrease coverage by 0.21%. The diff coverage is 80.00%.

@@            Coverage Diff             @@
##           master     #270      +/-   ##
==========================================
- Coverage   99.79%   99.59%   -0.21%     
==========================================
  Files          26       27       +1     
  Lines         484      489       +5     
==========================================
+ Hits          483      487       +4     
- Misses          1        2       +1     

Impacted Files	Coverage Δ
...ee/api/payments/source_views/_stripe.json.jbuilder	80.00% <80.00%> (ø)

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