RouterFS: Add support for multiple default FileSystem implementations

[Jonathan-Rosenberg]

For each configured mapping there will be a mandatory requirement to add a default FileSystem implementation mapping. For example: For the following mappings:

routerfs.mapping.s3a.1.replace=s3a://bucket/dir1/
routerfs.mapping.s3a.1.with=lakefs://router/main/
routerfs.mapping.blablabla.1.replace=blablabla://bucket/dir2/
routerfs.mapping.blablabla.1.with=lakefs://router/dev/path

We'll also need to configure default FileSystem implementation mappings:

routerfs.default.fs.s3a=org.apache.hadoop.fs.s3a.S3AFileSystem
routerfs.default.fs.blablabla=org.apache.hadoop.fs.s3native.NativeS3FileSystem

[talSofer]

@Jonathan-Rosenberg can we close this issue? I think it was already implemented

[Jonathan-Rosenberg]

Absolutely