Fix POST \dns\blocking request documentation

[akordowski]

What does this PR aim to accomplish?:

This PR fixes the documentation for the POST \dns\blocking request as described in the #1844 issue.

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[DL6ER]

Thank you for your PR which is good to be merged in principle but DCO is complaining, see here: https://github.com/pi-hole/FTL/pull/1846/checks?check_run_id=19983617941

Commit sha: 9b7647e, Author: Artur Kordowski, Committer: Artur Kordowski; Expected "Artur Kordowski [email protected]", but got "akordowski [email protected]".

[akordowski]

@DL6ER Yes, I have seen and fixed it.

[DL6ER]

@akordowski sorry for the huge delay. The FTL repository requires the commits to be signed for authenticity. Do you want to do this (and be prepared for future PRs also to other open source projects) or would you rather like me to cherry-pick them and sign the commits with my key setup?

It's not a lot of work, you can find info at https://docs.github.com/articles/about-gpg/ or (more strep-by-step like) in other tutorials on the web

[akordowski]

@DL6ER I have currently little time. So if it can wait till next week I can do it, otherwise feel free to cherry-pick the commit and complete the PR. Thank you!

[akordowski]

@DL6ER I managed to set all up and sign the commit. Please approve the PR again. Thank you!