Edit this page + ToC design

[zbayoff]

(Reopened from #5655)

1. Adds Edit button in TOC which will link to the source md file in github, if it exists. If there is no md file, as would be the case for integrations, the Edit button links to open a new issue in Github.
2. Updates the Mobile and Desktop TOC design. The TOC should now always be visible on desktop (if not disabled), and will be toggleable on mobile.
3. The .mainContent-wrapper column is reduced from the current 9 columns to 7 columns for better readability. The 12 column layout is now 3 (sidenav) - 7 (main Content) - 2 (TOC). There may be a couple layout issues regarding tabs fitting into the smaller column width.

https://trello.com/c/XbTcdAlX/3367-add-dependencies-in-all-public-documentation-page

https://docs-staging.datadoghq.com/zach/editPage/

[zbayoff]

#5655 (comment)

[ruthnaebeck]

It should be possible to disable the TOC and have pages stretch for the main integration page and landing pages (example).

For the integrations located in dogweb we should direct people to https://github.com/DataDog/documentation/issues/new?template=issue.md instead of https://github.com/DataDog/documentation/issues/new/choose. Also, can we check if there's a way to populate the referring URL into the GitHub text box?

Is there a way to handle pages that get combined (example)?

[ruthnaebeck]

LGTM 🙂