docs(py): add pip-based install tutorial #27943
- New tutorial: `doc/tutorials/py_tutorials/py_setup/py_pip_install/py_pip_install.markdown` with anchor `{#tutorial_py_pip_install}`.
- Python setup TOC updated to include the new page near the top.
- Windows/Ubuntu/Fedora pages: added **Quick start (pip)** callout
- Expanded troubleshooting in the pip tutorial (env mismatch, headless GUI notes, wheel mismatches, Raspberry Pi/ARM guidance).
This aligns with the issue request to make `pip install opencv-python` the default path for Python newcomers and reduce confusion from legacy content.
Fixes#24360
### Pull Request Readiness Checklist
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
omaraziz255