Inconsistency in namespacing of intentions between CLI and UI

**Old UI or New UI**

Consul 1.10.0+ent with new, new UI

**Describe the problem you're having**

On the CLI, `consul intention list` only shows intentions from the currently selected namespace, or `default` namespace if one is not defined. In the UI, regardless of which namespace is actively selected, the intentions view shows intentions from all namespaces, and changing the actively selected namespace has no effect.

This clutters up the webui, making it harder for users to manage intentions for their own services because they're crowded out by intentions relating to other teams/namespaces.

**Describe the solution you'd like**

Intentions list in the UI should be filtered based on the active namespace, just like other UI views such as services, tokens, policies etc are.

No files or tests are named in the issue. Start by locating the intentions view and the active-namespace handling used by the services, tokens, or policies views; compare how their data is filtered. Done means the intentions view shows only intentions from the selected namespace and changes when the active namespace changes.

Written by the indexing model from the issue text.