Implement RouterFS's file system operations

[talSofer]

After adding a mapping capability RouerFS can use, this task is to implement RouterFS filesystem operations using the Path mapper.

Definition of done

• RouteFS translates paths into their desired form
• RouteFS fetches the correct file system for the translated path at runtime. (correct = configured for the relevant fromSchema)
• RouterFS uses the relevant filesystem to invoke filesystem operations.
• Spark users that build RouterFS locally can access lakeFS (via s3 gateway) and s3 from a spark application that does not include lakeFS-style paths.
• The bullet above holds for any underlying object store supported by lakeFS, and for any combination of underlying stores.
• RouterFS's code is unit-tested

[arielshaqed]

First part is in #3327.