R1:48e121c485a2

Config Projects Extra Fields: link to the doc (like User)

Summary:
Add a documentation link in a specific Config page, that is:

Config > Setting > projects.custom-field-definitions

Comparison example:

| User | People |
|-----------|------------|
|{F1633919} | {F1633920} |

This change is a boring follow-up of this one:

https://we.phorge.it/D25507

Test Plan:
Visit the page and click on the new link:

- /config/edit/projects.custom-field-definitions/

Visit this page that was the inspirational…