Document column limitations

[jessejlt]

Columns of type dynamic have a default size limitation of 1MiB https://learn.microsoft.com/en-us/kusto/query/scalar-data-types/dynamic . In the case of the operator component, when creating heartbeat rows that contain schemas that exceed the default 1MiB limit, a null is inserted instead of truncating the result. If a user encounters this, they can create a ManagementCommand like

apiVersion: adx-mon.azure.com/v1
kind: ManagementCommand
metadata:
  name: heartbeat-schema-bigobject32
  namespace: adx-mon
spec:
  database: "<your-heartbeat-database>"
  body: |
    .alter column <HeartbeatTable>.Schema policy encoding type='BigObject32'

that will enable the schemas to grow out to 32MiB before they hit the column limitation.

Update the operator documentation for the described limitation and workaround.

[copilot-swe-agent]

The agent encountered an error and was unable to start working on this issue: Before you can use Copilot cloud agent, you need to pick a "Usage billed to" option in your Copilot settings. Update your settings, then try again. (Request id: F708:1CE166:188C58:18A75A:69D52413)