Refactor: remove Version.documentation_type

[humitos]

We are planning to support any doctool and we want to get rid of the documentation_type attribute and make our logic more generic to work on most scenarios without specific logic per doctool.

[humitos]

Summarizing the required changes here:

• EmbedAPIv1 needs to be removed since it uses documentation_type to decide how to parse the file. It seems that /api/v1/embed/ and /api/v2/embed hit the same code. I took a look at CF and there are some users already using v2: https://dash.cloudflare.com/76f653d51b8df4e9e956eb83a5ff42f4/readthedocs.org/analytics
  /traffic?path~starts=%2Fapi%2Fv2%2Fembed%2F&time-window=43200. We will need a plan to deprecate it.
  • https://docs.tweepy.org/ uses an old version of sphinx-hoverxref that hits /api/v2/embed/
  • https://docs.poliastro.space/ it's in the same situation
  • there are other projects we should contact before deprecating this endpoint
• Footer API is using it to generate a path and remove the /index part of the URL when it's Sphinx HTMLDIR or MKDOCS. It may makes sense to review this logic because I'm not 100% sure how it works and why it's needed. Also, this endpoint will be replaced by the new Addons flyout and its /_/readthedocs-config/ API endpoint.
• The same logic about striping the index.html is used in the PageSearchSerializer APIv2 serializer.
• Telemetry data collector use this type to decide whether or not collecting Sphinx specific data. This code could easily be adapted by checking for the existence telemetry.json file instead.
• We require Search: Only use generic parsers #10272 to always use the GenericParser to create search indexes.

It seems the only blocker here is "understanding the logic behind the stripping of index.html from FooterAPI and PageSearchSerializer. Then, we can re-write that logic to not be based on the doctype or remove it completely if it's not required.

I think we are close to be able to move forward here.

[humitos]

Related:

• Embed API: fully deprecate/remove embed API V2 #10677
• Post: enable addons by default website#308