Add/update documentation for product prefill #14874

Job	Run time
Build and check documentation	3m 27s
End-to-end tests, chromium	14m 17s
End-to-end tests, firefox	17m 25s
Run the Django test suite	7m 53s
End-to-end tests, webkit	12m 42s
Run the Django test suite in reverse	5m 38s
Set up docker build 'dynamic' env variables	1s
docker_build (production) / Build image	2m 49s
docker_build (extensions, token_exchange,prefill_haalcentraalhr, all-extensions-) / Build image	2m 50s
Simulate upgrading instances (2.7.4)	1m 39s
Simulate upgrading instances (2.7.8)	1m 29s
Scan docker image	2m 5s
Check for unexepected OAS changes	0s
Generate Postman collection from OAS	0s
Generate SDKs from OAS	0s
Validate OAS	0s
Push Docker image	0s
update-docker-readme	0s
	1h 12m 15s

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