Protect against concurrent duplicated webhooks

[waiting-for-dev]

Summary

By acquiring an update lock on the payment, we can ensure that only one concurrent excecution of the webhook handler will manipulate it. That will avoid duplicated log entries and obscure exceptions.

Closes #188

Checklist

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[codecov[bot]]

Codecov Report

Merging #285 (7bd100c) into master (b04dedd) will not change coverage. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #285   +/-   ##
=======================================
  Coverage   99.59%   99.59%           
=======================================
  Files          27       27           
  Lines         489      489           
=======================================
  Hits          487      487           
  Misses          2        2           

Impacted Files	Coverage Δ
...olidus_stripe/webhook/payment_intent_subscriber.rb	100.00% <100.00%> (ø)

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[waiting-for-dev]

Sorry, replaced by #286