[try-cb-nodejs] Update sample app to support 'agent' scope

Repo: https://github.com/couchbaselabs/try-cb-python
Branch to merge changes in: 7.0 (it might need to be created)

Based on the diagram shown in the Travel Sample doc here:

https://docs.google.com/document/d/1guGlXw07dLNtw-d6W_h9Gv_Ol7mo9z6L2SPtlGdj1qs/edit

We should update the try-cb-nodejs sample app to use the new 'Tenant_Agent' scopes and showcase multi-tenancy with scopes and collections.

There will be some changes applied on the FE, so we will need to update the 'static' directory in the project. The ticket for the FE changes is DOC-8135