Branding main to .NET8 alpha 1 (#6906)

eng/Versions.props

 <?xml version="1.0" encoding="utf-8"?>
 <Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <PropertyGroup>
-    <MajorVersion>7</MajorVersion>
+    <MajorVersion>8</MajorVersion>
     <MinorVersion>0</MinorVersion>
     <PatchVersion>0</PatchVersion>
-    <PreReleaseVersionLabel>rc</PreReleaseVersionLabel>
-    <PreReleaseVersionIteration>2</PreReleaseVersionIteration>
+    <PreReleaseVersionLabel>alpha</PreReleaseVersionLabel>
+    <PreReleaseVersionIteration>1</PreReleaseVersionIteration>
     <VersionPrefix>$(MajorVersion).$(MinorVersion).$(PatchVersion)</VersionPrefix>
     <!--
       Set assembly version to align with major and minor version, as for the patches and revisions should be manually