Ability to configure Sentry options at the namespace level

[seanhoughtonatvi]

Problem

Sentry recommends (see this video]) a fine-grained project structure. This usually means that multiple Sentry projects are represented within a single Kubernetes cluster.

Currently this requires one of two options

1. Run an instance of sentry-kubernetes in every namespace and use the SENTRY_K8S_WATCH_NAMESPACES option to select the single namespace.
2. Add the sentry.io/dsn label to every resource in the namespace

Request

Allow users to set the sentry.io/dsn and sentry.io/environment labels on the namespace. This would allow Kubernetes administrators to host the service and service administrators to opt-in to sending Sentry events for their projects with a simple label change.

Adding a new sentry.io/level label to control the logging level would be a bonus.

Thanks!