Stripe : move customer_data field to metadata

[fabienheureux]

Ref #378

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In stripe/providers.py the field customer_data does not seem to be defined in Stripe API's Session object

It could be moved to the metadata field (from Stripe's documentation) :

Set of key-value pairs that you can attach to an object. This can be useful for storing additional information about the object in a structured format.

[WhyNotHugo]

LGTM.

Needs rebase (has conflicts).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.42%. Comparing base (8303e09) to head (3c6177c).
Report is 15 commits behind head on main.

Additional details and impacted files

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  Coverage   78.42%   78.42%           
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  Files          29       29           
  Lines        1979     1979           
  Branches      244      234   -10     
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  Hits         1552     1552           
  Misses        310      310           
  Partials      117      117           

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