Change to Notification Endpoint not reflecting in Notification Rules

__Steps to reproduce:__
List the minimal actions needed to reproduce the behavior.

1. Create Notification Endpoint with associated Notification Rule
2. Change URL for Notification Endpoint
3. The associated Notification Rule continues to use the previous URL, only updating after editing and saving the Notification Rule (should not have to , )

__Expected behavior:__
Should update automatically

__Actual behavior:__
The notification rule does not automatically update when the notification endpoint changes.

__Environment info:__

* System info: `Linux 5.8.0-41-generic x86_64`
* InfluxDB version: `Influx CLI 2.0.3 (git: fe04d346df) build_date: 2020-12-15T01:00:16Z`

No files, tests, or entry points are named. Reproduce the issue by changing a Notification Endpoint URL after creating its associated Notification Rule, then trace the endpoint and rule update paths; done means the rule uses the new URL without requiring a separate edit and save.

Written by the indexing model from the issue text.