Adding TOC to dbt_cloud_setup.md

[MekongDelta-mind]

What change?

Adding the Table of contents to the dbt_cloud_setup.md markdown for navigating easily through the page.

Why the change ?

As the content is long with all the images and instructions, it is a bit hard to navigate through the page. So adding the TOC at the top for easy navigation

Code changes ( if any )?

None. Only Markdown file is changed.