Create Visual Studio extension to add item to Git History page

I'm working on trying to create a Visual Studio 2019 extension. I'd like to add an additional option to the context menu when clicking on a commit in the history. Then from there I'd like to grab a snapshot of the files that were changed in that commit both before and after. I'm having trouble getting the button added to the context menu.

I've installed the Command Explorer and was able to find the reference to the context menu.

However, when I add a reference to it in my .vsct file it can't find it.

<Group guid="guidSubmitVulnerabilityCmdSet" id="GitMenu" priority="0x0600">
        <Parent guid="PackageCommandSetGuid" id="GitHistory_ContextMenu" />
      </Group>

I figured I needed to add an Extern element with a reference to the proper header file, but I can't find any .h file on my system that contains these values. I've also tried looking through the Microsoft.TeamFoundation.Git.Provider.dll assembly in the Object Explorer, but didn't see anything promising.

This is the context menu I'm trying to extend.

Is what I'm trying to do possible, or is the Git History page built in a way that it can not be extended?

Thanks in advance for any help!

For those who may be looking to do something similar this is what I added.

<GuidSymbol name="PackageCommandSetGuid" value="{57735d06-c920-4415-a2e0-7d6e6fbdfa99}">
  <IDSymbol value="0xf040" name="GitHistory_ContextMenu" />
</GuidSymbol>

Here is the resulting context menu looks like with my button added to the bottom.