docs: updates ticket annotations for block structure settings and toggles

Updates the annotations for the block structure settings and toggles based on a [discussion] that was held on the pull request that annotated those same settings and toggles.

It also adds the DEPR tickets that were promised earlier in the annotations.
For future reference, there's also a [forum thread] to discuss the DEPR tickets titled.

[discussion]: https://github.com/edx/edx-platform/pull/26175#issuecomment-800632485

[forum thread]: https://discuss.openedx.org/t/deprecation-removal-several-block-structure-caching-settings-depr-143-depr-144-depr-145-depr-146/4288?u=nizar