Alert timeseries visualization trend should not disable when alert silenced.

### Problem Statement

One reason to silence an alert is because it is too noisy and work is being done to resolve the issue/issues that is causing the noise. Later when the root cause is resolved the alert will be un-silenced.

Today, when you silence an alert the Alert timeseries visualization is disabled with a notification that the alert state is currently muted. see image below


Knowing how many alerts would have fired while in the muted state and/or seeing dip in alerts in the muted state helps me determine if the alert is less noisy and can be re-enabled (unmuted). (To do this today I clone the alert and disable the notifications, just so i can see the trend and how it is changing/safe to reenable without annoying people)

### Solution Brainstorm

What I would like to see is on the alert triggered timeseries is: (see image below)
- show annotations when the alert was muted and unmuted.
- color the background different if the time period is muted vs. unmuted
- the visualization to remain enabled and collecting data while in the muted state.


### Product Area

Alerts