chore: Fix props to support more than one project

Ran across this while working on open-feature/dotnet-sdk-contrib#127,
and tldr; if there's more than one project under `src/`, having the
`<PackageId>` hard-coded in `build/Common.prod.props` causes MSBuild
to panic.

There are two options to fix this:

1. ```diff
   - <PackageId>OpenFeature</PackageId>
   + <PackageId>$(MSBuildProjectName)</PackageId>
   ```
2. ```diff
   - <PackageId>OpenFeature</PackageId>
   ```

Since NuGet defaults `PackageId` to the assembly name, I'm opting
for (2), but if I've overlooked some nuance/custom build steps that
require setting `PackageId` explicitly, then we could just as well
fallback to (1).

Signed-off-by: Austin Drenski <austin@austindrenski.io>

.github/workflows/release.yml

@@ -42,7 +42,7 @@ jobs:
       - name: Pack
         if: ${{ steps.release.outputs.releases_created }}
         run:  |
-          dotnet pack OpenFeature.proj --configuration Release --no-build -p:PackageID=OpenFeature
+          dotnet pack OpenFeature.proj --configuration Release --no-build
 
       - name: Publish to Nuget
         if: ${{ steps.release.outputs.releases_created }}

build/Common.prod.props

@@ -11,7 +11,6 @@
     <RepositoryUrl>https://github.com/open-feature/dotnet-sdk</RepositoryUrl>
     <Description>OpenFeature is an open standard for feature flag management, created to support a robust feature flag ecosystem using cloud native technologies. OpenFeature will provide a unified API and SDK, and a developer-first, cloud-native implementation, with extensibility for open source and commercial offerings.</Description>
     <PackageTags>Feature;OpenFeature;Flags;</PackageTags>
-    <PackageId>OpenFeature</PackageId>
     <PackageIcon>openfeature-icon.png</PackageIcon>
     <PackageProjectUrl>https://openfeature.dev</PackageProjectUrl>
     <PackageLicenseExpression>Apache-2.0</PackageLicenseExpression>