Fix Failing edx-platform Docs Builds

[feanil]

The edx-platform docs build keeps getting terminated on ReadTheDocs because of excessive memory consumption.

Example: https://readthedocs.org/projects/edx-platform-docs/builds/26209149/

We've already hit the limit on the amount of resource increases RTD will give us so we need to figure out how we can reduce our resource consumption for these builds so that they build quickly.

RTD suggested reviewing this doc to help us reduce resource consumption: https://docs.readthedocs.io/en/latest/guides/build-using-too-many-resources.html

[feoh]

Hi. Just to be clear this is blocking the Sumac release notes effort. We use the docs build to generate a list of new waffle tags per release.

[irtazaakram]

@feanil I don't know what to make of this: https://readthedocs.org/projects/edx-platform-docs/builds/26317625/

[feanil]

I think the issue is that it still takes a really long time to build and while it's building it does not provide much output. Are there other ways we could speed up the build?

[irtazaakram]

#35939
The only way I could get these docs to pass was by limiting the directories. Any other approach makes the process too long for the Read the Docs server.