Ensure contentFiles are unobtrusive in code editors

This ensures the instrumentation scripts are not visible users projects when they reference `OpenTelemetry.AutoInstrumentation`.

This makes the manual installation route slightly less unobtrusive as we don't clutter anyones editor with instrumentation.sh and instrumentation.cmd.

These files will still be published to output and publish directories.

The props file is only necessary until NuGet/Home#4856 gets resolved.

See: https://learn.microsoft.com/en-us/nuget/concepts/msbuild-props-and-targets for more background on how $PROJECT.props file affect nuget installations.

nuget/OpenTelemetry.AutoInstrumentation/build/opentelemetry.autoinstrumentation.props

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+<!-- Hide the shipped content files VS project tree.
+     Can be removed once https://github.com/NuGet/Home/issues/4856 is resolved -->
+<ItemGroup>
+  <Content Update="@(Content)">
+    <Visible Condition="'%(NuGetItemType)' == 'Content' and '%(NuGetPackageId)' == 'opentelemetry.autoinstrumentation'">False</Visible>
+    <CopyToOutputDirectory Condition="'%(NuGetItemType)' == 'Content' and '%(NuGetPackageId)' == 'opentelemetry.autoinstrumentation'">Always</CopyToOutputDirectory>
+    <CopyToPublishDirectory Condition="'%(NuGetItemType)' == 'Content' and '%(NuGetPackageId)' == 'opentelemetry.autoinstrumentation'">Always</CopyToPublishDirectory>
+  </Content>
+</ItemGroup>
+</Project>