Add option to set y-axis minimum value of test result trend

### What feature do you want to see added?

Right now, you can't change the minimum y-axis value in the test result trend. The plugin sets it automatically, which can sometimes be misleading. For example, it might look like most tests have failed, when actually most have passed.


Could you add an option to manually adjust the y-axis minimum value?

### Upstream changes

_No response_

### Are you interested in contributing this feature?

_No response_

Start by locating the test result trend chart and the existing option or configuration that controls its y-axis. Add a user-configurable minimum value, then verify that the trend uses it and that the default behavior remains unchanged.

Written by the indexing model from the issue text.