topicHref for generated metadata only works if the file is in the dest folder

**Operating System**: Windows

**DocFX Version Used**: 2.58

**Template used**: default

````docfx metadata```` generates .yml files including toc.yml to ````dest```` folder. Including this folder in the main ````toc.yml```` adds the generated .yml to the top navigation bar. Using ````topicHref```` to refer to a .md file in the ````dest```` folder is nicely display as the first page for that api, with the toc sidebar on the left. Using ````topicHref```` to refer to a .md file elsewhere it is displayed without the toc sidebar and there is now no way to get to a page that has the toc sidebar.

My problem is this: I don't want any non-generated files in the ````dest```` folder, I want to be able to delete this folder as I please (I will have to run ````docfx metadata```` again), and I want to exclude the generated .yml files from git. Is there a way to do that and still have an intro page to the api?

Reproduce the behavior with DocFX 2.58, the default template, generated metadata in dest, and topicHref pointing to a Markdown file inside and outside dest. Start with the metadata and navigation handling involved in docfx metadata and topicHref. Done means an external intro page can retain the API toc sidebar while dest contains only generated files.

Written by the indexing model from the issue text.