Relative markdown links between blog and docs does not work

### Have you read the Contributing Guidelines on issues?

- [X] I have read the [Contributing Guidelines on issues](https://github.com/facebook/docusaurus/blob/main/CONTRIBUTING.md#issues).

### Prerequisites

- [X] I'm using the latest version of Docusaurus.
- [X] I have tried the `npm run clear` or `yarn clear` command.
- [X] I have tried `rm -rf node_modules yarn.lock package-lock.json` and re-installing packages.
- [X] I have tried creating a repro with https://new.docusaurus.io.
- [X] I have read the console error message carefully (if applicable).

### Description

Hi Docusaurus team,

Love this library - thank you for your awesome work!

I'm looking to link a blog post to a docs page using a relative markdown link, but I receive the following error when I specify `[link to doc](../../docs/doc-page.md)` in the blog post:

`[WARNING] Blog markdown link couldn't be resolved: (../../docs/doc-page.md) in "/home/projects/github-dc5ygn/blog/blog-post.md`

On the other hand, using link without the `.md` (`[link to doc](../../docs/doc-page)`) extension works fine.

Is there a way I can prevent the broken link while preserving the `.md` extension? I'm using an Obsidian plugin to convert wikilinks to internal links and need to keep the `.md` extension for it to work properly.

### Reproducible demo

https://stackblitz.com/edit/facebook-docusaurus-mx3fkh?file=blog%2Fblog-post.md

### Steps to reproduce

1. Go to demo linked above.
2. Wait for the site to compile. You should see a warning: `[WARNING] Docs markdown link couldn't be resolved: (../../docs/doc-page.md) in "/home/projects/facebook-docusaurus-mx3fkh/docs/doc-page.md" for version current`
3. In the website preview on the right, click the menu button (three bars).
4. Click **Blog**.
5. Under the "blog-post" title click **"link to doc"**.
6. You should see a "Page Not Found" error.
7. Edit "blog-post.md" to exclude ".md" from the link: `[link to doc](../../docs/doc-page)`
8. Complete steps 2-5. Link should now work correctly.

### Expected behavior

The link `[link to doc](../../docs/doc-page)` should work regardless of whether or not `.md` is specified.

### Actual behavior

The link `[link to doc](../../docs/doc-page)` only works when `.md` is omitted.

### Your environment

- Public source code: See demo link above
- Public site URL: See demo link above
- Docusaurus version used: 2.4.1
- Environment name and version (e.g. Chrome 89, Node.js 16.4): Node.js 16.20.0
- Operating system and version (e.g. Ubuntu 20.04.2 LTS): N/A

### Self-service

- [ ] I'd be willing to fix this bug myself.