Add a sticky content navigation on the right side

[contaoacademy]

To jump more quickly to the individual sub-items on a page, the TOC should appear sticky on the right-hand side from a viewport of 1800px.

Task for @fritzmg

[contaoacademy]

Maybe it is a good idea to push this PR to get implemented?
matcornic/hugo-theme-learn#101

[fritzmg]

Maybe it is a good idea to push this PR to get implemented?

That's not really how Open Source works - or is supposed to work ;).

[contaoacademy]

🤔 My wording was a bit unfortunate.
Decide for yourself whether it is better to wait for the PR or to implement it yourself.

[fkaminski]

Maybe it is a good idea to push this PR to get implemented?

FYI: The currently used "Hugo Learn Theme" (https://github.com/matcornic/hugo-theme-learn) is deprecated and no longer maintained ... (See #1462).