Added theme_switcher 
Added theme_switcher in  navbar_end to display the Dark/Light theme switcher

- [x] closes #48598 (Replace xxxx with the Github issue number)
- [x] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [x] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

In Python you need to leave one space after commas. You can use flake8 to validate that there are no issies with the style of your code. That will make the checks green. Thanks @deepaksirohiwal, looks good to me. Did you try this locally? Do you mind adding a screenshot here, so others can see how this will look when merged please? Here are some screenshots of the new visual changes. Now Theme switch is available (top right) to toggle between different modes (Dark, Light and Auto) 
1
![Light](https://user-images.githubusercontent.com/38135521/191915680-3cc5fe32-8ca9-49e2-9a24-082b543af79c.jpg)
Light mode-Switch
2
![dark](https://user-images.githubusercontent.com/38135521/191915796-b98c8988-ccd1-4cd3-8e03-852950d92f12.jpg)
Dark mode -Switch
3
![auto](https://user-images.githubusercontent.com/38135521/191916103-0b6aab7c-5609-4dd5-9600-847b86c68ad1.jpg)

Auto mode(according to system setting)-Switch
 thank you so much the dark theme is so hard to read in the docs! Thanks @deepaksirohiwal  Thank you @datapythonista and @mroeschke, I really learnt a lot and would love to contribute more. 