Specify DataGridRowHoveredBackgroundColor beyond SystemListLowColor (#3826)

## Fixes #
#3825

Specifies the hover color for DataGridRows in a seperate resource to prevent overriding SystemListLowColor

## PR Type
What kind of change does this PR introduce?
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<!-- - Bugfix -->
 Feature
<!-- - Code style update (formatting) -->
<!-- - Refactoring (no functional changes, no api changes) -->
<!-- - Build or CI related changes -->
<!-- - Documentation content changes -->
<!-- - Sample app changes -->
<!-- - Other... Please describe: -->


## What is the current behavior?
Row hover color in DataGrid is decided by `SystemListLowColor`


## What is the new behavior?
Row hover color in DataGrid is decided by `DataGridRowHoveredBackgroundColor` which defaults to `SystemListLowColor`

## PR Checklist

Please check if your PR fulfills the following requirements:

- [X] Tested code with current [supported SDKs](../readme.md#supported)
- [x] Pull Request has been submitted to the documentation repository [instructions](..\contributing.md#docs). Link: <!-- docs PR link -->
- [x] Sample in sample app has been added / updated (for bug fixes / features)
    - [x] Icon has been created (if new sample) following the [Thumbnail Style Guide and templates](https://github.com/windows-toolkit/WindowsCommunityToolkit-design-assets)
- [x] New major technical changes in the toolkit have or will be added to the [Wiki](https://github.com/windows-toolkit/WindowsCommunityToolkit/wiki) e.g. build changes, source generators, testing infrastructure, sample creation changes, etc...
- [x] Tests for the changes have been added (for bug fixes / features) (if applicable)
- [x] Header has been added to all new source files (run *build/UpdateHeaders.bat*)
- [x] Contains **NO** breaking changes


## Other information

Author: msftbot[bot]

Microsoft.Toolkit.Uwp.UI.Controls.DataGrid/DataGrid/DataGrid.xaml

@@ -89,6 +89,7 @@
     <StaticResource x:Key="DataGridRowSelectedUnfocusedBackgroundOpacity" ResourceKey="ListAccentLowOpacity"/>
     <StaticResource x:Key="DataGridRowSelectedHoveredUnfocusedBackgroundColor" ResourceKey="SystemAccentColor"/>
     <StaticResource x:Key="DataGridRowSelectedHoveredUnfocusedBackgroundOpacity" ResourceKey="ListAccentMediumOpacity"/>
+    <StaticResource x:Key="DataGridRowHoveredBackgroundColor" ResourceKey="SystemListLowColor"/>
     <StaticResource x:Key="DataGridRowHeaderForegroundBrush" ResourceKey="SystemControlForegroundBaseMediumBrush"/>
     <StaticResource x:Key="DataGridRowHeaderBackgroundBrush" ResourceKey="SystemControlBackgroundAltHighBrush"/>
     <StaticResource x:Key="DataGridRowGroupHeaderBackgroundBrush" ResourceKey="SystemControlBackgroundChromeMediumBrush"/>
@@ -597,7 +598,7 @@
                                 <VisualState x:Name="NormalAlternatingRow"/>
                                 <VisualState x:Name="PointerOver">
                                     <Storyboard>
-                                        <ColorAnimation Storyboard.TargetName="BackgroundRectangle" Storyboard.TargetProperty="(Shape.Fill).(SolidColorBrush.Color)" Duration="0" To="{ThemeResource SystemListLowColor}"/>
+                                        <ColorAnimation Storyboard.TargetName="BackgroundRectangle" Storyboard.TargetProperty="(Shape.Fill).(SolidColorBrush.Color)" Duration="0" To="{ThemeResource DataGridRowHoveredBackgroundColor}"/>
                                     </Storyboard>
                                 </VisualState>
                                 <VisualState x:Name="NormalSelected">