feat: add switch to disable dns pinning

[kesselb]

Summary

⚠️ One should not disable DNS pinning unless they know what they are doing

A hard requirement for DNS pinning is the ability to resolve DNS records.
If resolving DNS records is not possible, DNS pinning cannot work.

HTTP proxy => DNS names are resolved via proxy (c.f. https://everything.curl.dev/libcurl/proxies#local-or-proxy-name-lookup). That explains, why outgoing connections work without the possibility to resolve DNS records locally.

TODO

• CI

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[kesselb]

/backport to stable27

[kesselb]

/backport to stable26

[Altahrim]

A bit sad to come to this, but I don't have a better solution for now ^^

[backportbot-nextcloud]

The backport to stable26 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable26
git pull origin stable26

# Create the new backport branch
git checkout -b fix/foo-stable26

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts. Resolve them.
git cherry-pick abc123

# Push the cherry pick commit to the remote repository and open a pull request
git push origin fix/foo-stable26

More info at https://docs.nextcloud.com/server/latest/developer_manual/getting_started/development_process.html#manual-backport

[mgallien]

/backport to stable25