Make index_page configurable

[noelmcloughlin]

I would like index_page: <readme-or-some-other-name>.md feature. While #608 is concerned with readme.md I see different problem. Index is a semantic concept in various ontologys and also wikidata KG (here, here, here).

The LinkML (life sciences mainly) community model concepts in schemas for various domains. Today I was modeling index slot/propety and mkdocs generates two index.md and second overwrites first. Since the slot/property index is entrenched in various ontologies - using another name is not possible.

Please add flexibility for index.md to support semantic use cases, where "index" is a thing outside mkdocs project.

[lovelydinosaur]

I'm going to push this into a discussion, rather than an issue for now.

Perhaps you could expand on exactly what behavior you're asking for here. We use index.md because it maps to index.html which is what webservers expect.