Add table of contents support to ecosystem page
This PR adds a table of contents to the Ecosystem page using the Markdown `TocExtension`.

- Inserted `[TOC]` placeholder in `ecosystem.md`
- Enabled `toc` extension in `web.py`
- Configured `toc_depth` for h2 and h3 headers
- Closes #61587

@akafle01 do you have time to continue the work on this? > @akafle01 do you have time to continue the work on this?

Yes I will work on it today /preview Website preview of this PR available at: https://pandas.pydata.org/preview/pandas-dev/pandas/61595/ Thanks @akafle01 for the contribution. I was checking this, as the table of contents looked different than in the other pages, and realized besides adding the ToC we needed to do some refactoring. I better add the ToC to Ecosystem in #61655 where I've implemented the refactor, so we can test both things together.

I'll close this PR, sorry about it, as the work you've been doing is great, just more practical to add this in the other PR.