feat: consider namespace when managing watcher

[Ramilito]

Fixes: #656

This will improve performance by requesting a subset of items when only interested in a specific namespace.
The All namespace will work as before.

Things to consider:

• will this create a lot of watchers? - solved by deleting them when using All
• will this be slower in the end? need to reload for every namespace change? - sort of, each new namespace will have a new watcher, also solved by using All