[#2804] Update headers for requests with Haal Centraal API client

[pi-sigma]

We need to pass additional headers for requests made with the Haal Centraal API client (these are not required by the API itself, but needed for integration of other services in connection with the API, e.g. PinkRoccade):

• x-origin-oin
• x-doelbinding
• x-verwerking
• x-gebruiker

Taiga: https://taiga.maykinmedia.nl/project/open-inwoner/task/2804

See also the implementation in Open Forms: open-formulieren/open-forms#3731

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 95.45455% with 2 lines in your changes missing coverage. Please review.

Project coverage is 94.58%. Comparing base (df9656f) to head (788a34d).

Files with missing lines	Patch %	Lines
src/open_inwoner/haalcentraal/validators.py	60.00%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1438   +/-   ##
========================================
  Coverage    94.58%   94.58%           
========================================
  Files         1069     1071    +2     
  Lines        39623    39665   +42     
========================================
+ Hits         37478    37518   +40     
- Misses        2145     2147    +2     

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[pi-sigma]

@alextreme I added a field to the Haal Centraal configuration for the x-verwerking header, as well, in conformity with the Open Forms implementation (open-formulieren/open-forms#3731). Is this useful, or do we know for sure that we don't need this?

[alextreme]

@pi-sigma I'm not sure what the purpose of x-verwerking is, so having this working the same as OF seems like a smart idea

[swrichards]

I suspect this is taken care of by using the json kwarg to the post below, though I am not sure about the Accept (perhaps they also deal in XML?), so we might want to keep that.

[pi-sigma]

You're right about "Content-Type", this is handled by the requests library. The "Accept" header is not, so I'm keeping this.

[alextreme]

Okay, it may have been a bit more flexible if GebruikerZelf could also have been made configurable