nsfs: phase-1

[guymguym]

Explain the changes

1. This is still EXPERIMENTAL and the first phase still has TODO's left to be addressed.
2. Started with namespace_fs POC code from PR NS-FS: Namespace over a shared Filesystem - WIP #6077.
3. Implement deep list-objects.
4. Add npm run build:core to build the noobaa-core standalone program.
5. noobaa-core nsfs ... command will run nsfs in standalone mode.

Issues: Fixed #xxx / Gap #xxx

1. NA

Testing Instructions:

1. Test regression first - mainly of namespaces such as namespace S3.
2. Testing nsfs is easiest using noobaa-core nsfs or node src/core nsfs for dev env.