♻️ [open-formulieren/open-forms#4398] Cache initialDataReference to pass it with submissionCreate

[stevenbal]

required for open-formulieren/open-forms#4696

previously this was not passed properly, resulting in the initialDataReference not being sent on submissionCreate

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.42%. Comparing base (06d6ac1) to head (3a202c0).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #716      +/-   ##
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- Coverage   77.63%   77.42%   -0.22%     
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  Files         234      234              
  Lines        4780     4784       +4     
  Branches     1301     1305       +4     
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- Hits         3711     3704       -7     
- Misses       1036     1047      +11     
  Partials       33       33              

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[sergei-maertens]

Discussed in the office:

• caching in session storage seems risky because it may re-use this reference in a completely different form
• ideal approach: baking in this parameter in the login link, so that it's sent to the backend and when the backend redirects again to the SDK, it should pass along the parameter again
• if we can not reliably obtain this parameter from the URL, we may need to grab it in App.js and store it in state (in-memory), and expose it via React.createContext
• make sure this works when the introduction page is enabled, which is a page before FormStart - it should not swallow the initial data reference query param

Good luck 🙂