Routes including index.html are broken

[rlamana]

🐛 Bug Report

In v1 URLs with and without index.html properly route to the same page. In v2 URLs including index.html will result in a "Page not found". react-router should use a pattern that matches both URLs.

Have you read the Contributing Guidelines on issues?

Yes.

To Reproduce

1. Navigate to https://v2.docusaurus.io/docs/introduction, the page should load normally.
2. Navigate to https://v2.docusaurus.io/docs/introduction/index.html, "Page not found" is displayed.

Expected behavior

Both https://v2.docusaurus.io/docs/introduction and https://v2.docusaurus.io/docs/introduction/index.html should take the user to the same page.

Actual Behavior

https://v2.docusaurus.io/docs/introduction/index.html renders this:

Your Environment

• Docusaurus version used: 2.0.0-alpha.48
• Environment name and version (e.g. Chrome 78.0.3904.108, Node.js 10.17.0): Node.js v10.19.0
• Operating system and version (desktop or mobile): MacOS X Catalina 10.15.2