In PSConfiguration.cs, WriteValueToFile() should check if value has changed before writing

# Summary of the new feature/enhancement

Currently, the [WriteValueToFile()](https://github.com/PowerShell/PowerShell/blob/75ba74cce6164d46bb85f561b4d657a56f1431f2/src/System.Management.Automation/engine/PSConfiguration.cs#L491) method always writes to the config file even if the value didn't change.  We could add logic to check if the value has changed before writing to the file.
