DOC: Reorganize Getting Started documentation pages
- [x] closes #32308 

Issue Related:
- `getting_started/index.html` removes `10 minutes to pandas`, `Essential basic functionality` and `Intro to data structures` from the toctree and moves them as links in `user_guide/index.html`
- `getting_started/tutorials.html` now only references community tutorials
- the pandas cheatsheet is now referenced at the bottom `Tutorial` section of `getting_started/index.html`

Misc:
- Lowercases `Pandas` to `pandas`
- Some rephrasing
