[FOLLOW UP] : Documentation optimizations for the new Sphinx structure #29220
### Pull Request Readiness Checklist
This PR serves as a follow-up to the new documentation system introduced in [#29206](https://github.com/opencv/opencv/pull/29206)
Co-authored by: @abhishek-gola @kirtijindal14 @Akansha-977 @Prasadayus @varun-jaiswal17
See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request
- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work
- [x] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
Patch to opencv_extra has the same branch name.
- [x] The feature is well documented and sample code can be built with the project CMake
Scripts for downloading models in DNN samples
* Initial commit. Utility classes and functions for downloading files
* updated download script
* Support YAML parsing, update download script and configs
* Fix problem with archived files
* fix models.yml
* Move download utilities to more appropriate place
* Fix script description
* Update README
* update utilities for broader range of files
* fix loading with no hashsum provided
* remove unnecessary import
* fix for Python2
* Add usage examples for downloadFile function
* Add more secure cache folder selection
* Remove trailing whitespaces
* Fix indentation
* Update function interface
* Change function for temp dir, change entry name in models.yml
* Update getCacheDirectory function call
* Return python implementation for cache directory selection, use more specific env variable
* Fix whitespace
omrope79
Alexander Smorkalov
Emmanuel Ferdman
Alexander Alekhin
Sergei Slashchinin
Alexander Alekhin
Dmitry Kurtaev