Enhanced Firewall Restrictions docs

Squashed commits:
[2081fc4] Enhanced Firewall Restrictions docs for PR symfony/symfony#10404
[8f065bc] Add redirect to new page
[b42e80f] fixed typos
[cc6b07d] tiny update
After backporting something from master (2.5), removing the 2.5-specific features
minor #3695 Firewall backport (weaverryan)

This PR was merged into the 2.4 branch.

Discussion
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Firewall backport

This backports the changes from #3681 with the 2.4-only changes.

After this is merged, we'll need to merge this into master (like normal). At that time, the 2.5-specific changes from the `firewall_restriction` and firewall configuration need to be added back.

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

Thanks!

Commits
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be46c76 After backporting something from master (2.5), removing the 2.5-specific features
9889dbe Enhanced Firewall Restrictions docs