Window period value for aggregating functions cannot be set for alerts

**Steps to reproduce:**

1. Start influxdb, create bucket, add measurements with numerical data fields
2. Create a check in the alerts page on one of the numerical data fields

**Expected behavior:**

On the define query page, I expect to be able to set the 'WINDOW PERIOD' field for the aggregate function, as is possible when querying data on the 'Expore Data' page.

**Actual behavior:**

I cannot set the 'WINDOW PERIOD' at all. It is stuck on it's auto value and greyed out.

I've had some people in the community (Reddit) suggest that changing the 'Schedule Every' field in the next page changes this window, and the documentation seems suggestive of this, too. However, changing the 'Schedule Every' field has no effect for me; the auto-window is stuck at seemingly random values, regardless of changes to 'Schedule Every'.

**Environment info:**

Docker Container: Linux 5.8.0-34-generic x86_64
Host machine: Linux 5.8.0-34-generic x86_64 (VM)
InfluxDB 2.0.3 (git: fe04d34) build_date: 2020-12-15T01:00:16Z