Allow remote disabling of sending events to Sentry in previously-published extension versions

### See https://github.com/confluentinc/vscode/discussions/353 for a detailed description of the feature flag mechanism

Depends upon #355 having been completed.

### Goals

Most of the time we want to send events to Sentry (assuming the user has not disable telemetry). However, in rare cases we may want to not send these events to Sentry. For example, a released version may have a bug that sends far too many events to Sentry, and we may want to disable the publishing of events for that specific version after it has been released. Or if we stop using Sentry, we might want to tell all versions to stop sending events to Sentry.

We can do this with the `ide.sentry.enable` feature flag, which will be `true` most of the time (including when LaunchDarkly is not reachable). However, when it is set to `false`, then we should not send events to Sentry.

### Questions:
Should we evaluate this flag just once (e.g., upon extension activation) and never again? Or should we check the flag every so often? We definitely should **not** check the flag every time we want to send an event.