Add/update documentation for product prefill #14837

Job	Run time
Set up docker build 'dynamic' env variables	1s
Build and check documentation	2m 53s
End-to-end tests, chromium	13m 20s
Run the Django test suite	7m 57s
End-to-end tests, firefox	16m 24s
End-to-end tests, webkit	12m 12s
Run the Django test suite in reverse	5m 33s
docker_build (production) / Build image	2m 56s
docker_build (extensions, token_exchange,prefill_haalcentraalhr, all-extensions-) / Build image	2m 47s
Scan docker image	2m 24s
Simulate upgrading instances (2.7.4)	1m 21s
Simulate upgrading instances (2.7.8)	1m 22s
Check for unexepected OAS changes	14s
Generate SDKs from OAS	43s
Generate Postman collection from OAS	21s
Validate OAS	13s
Push Docker image	0s
update-docker-readme	0s
	1h 10m 41s

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