Fix Image constraint class and validator link

Change Image constraint links from File and FileValidator to Image and ImageValidator.
bug #3747 Fix Image constraint class and validator link (weaverryan)

This PR was merged into the 2.3 branch.

Discussion
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Fix Image constraint class and validator link

Just a rebase of #3646...

Commits
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2a3955b Fix Image constraint class and validator link
fix literal
add missing toctree entry for the firewall restriction article
minor #3755 [Cookbook][Security] Firewall resitrction tweaks, fix markup, add to toc (xabbuh)

This PR was merged into the 2.4 branch.

Discussion
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[Cookbook][Security] Firewall resitrction tweaks, fix markup, add to toc

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.4+
| Fixed tickets |

Reapply some fixes to #3681 that probably got lost with #3695.

Commits
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612ab9b add missing toctree entry for the firewall restriction article
899bc4e fix literal
Merge branch '2.3' into 2.4
[Book][Internals] add description for the kernel.finish_request event