Add DevelopmentDependency property to CSharpier.MsBuild.csproj (#607

)

* Add `DevelopmentDependency` property to `CSharpier.MsBuild.csproj`

Hi, awesome project, thanks for your work!

This package only runs in `BeforeTargets="Build"` right? I just tested installing the MsBuild package like this (with PrivateAssets attr), in a global `Directory.Build.Props` file, and it seems to work:
```csproj
  <ItemGroup>
    <PackageReference Include="CSharpier.MsBuild" Version="0.15.0" PrivateAssets="all" /> 
  </ItemGroup>
```

Usecase being we have some packages that are going to be published, and we only need `csharpier` during build (doesnt need to be a dep of the package).

* Release as 0.15.1

Co-authored-by: Bela VanderVoort <bela.vandervoort@optimizely.com>

CHANGELOG.md

@@ -1,3 +1,9 @@
+# 0.15.1
+
+[diff](https://github.com/belav/csharpier/compare/0.15.0...0.15.1)
+
+- Set CSharpier.MsBuild as DevelopmentDependency. [#607](https://github.com/belav/csharpier/pull/607)
+
 # 0.15.0
 
 [diff](https://github.com/belav/csharpier/compare/0.14.0...0.15.0)

CSharpier.Build.props

@@ -1,6 +1,6 @@
 <Project>
     <PropertyGroup>
-        <Version>0.15.0</Version>
+        <Version>0.15.1</Version>
         <PackageLicenseExpression>MIT</PackageLicenseExpression>
         <RepositoryUrl>https://github.com/belav/csharpier</RepositoryUrl>
         <RepositoryType>git</RepositoryType>

Src/CSharpier.MsBuild/CSharpier.MsBuild.csproj

@@ -8,6 +8,7 @@
         -->
         <TargetFramework>netstandard2.0</TargetFramework>
         <PackageId>CSharpier.MsBuild</PackageId>
+        <DevelopmentDependency>true</DevelopmentDependency>
         <CSharpierOutputDir>../CSharpier.Cli/bin/$(Configuration)/net6.0</CSharpierOutputDir>
     </PropertyGroup>