Can't add maven local under `maven_install`'s repository

I'm trying to add maven local repository under `maven_install` but seems like it doesn't support this currently.

What I did is
```
maven_install(
name = "mvn",
artifacts = [
# Add all Android third-party deps here:
],
repositories = [
"https://maven.google.com",
"file://localpath",
],
version_conflict_policy = "pinned",
)
```
The file:// path will not be recognized

Start by tracing the maven_install repository handling for the file://localpath entry shown in the issue. Add coverage for a local Maven repository and verify that artifacts can be resolved from it without breaking the existing HTTPS repository behavior.

Written by the indexing model from the issue text.