feat(NuGet): Support NuGet GitHub Packages (#18)

* support pushing NuGet packages to GitHub packages

* alternate conflict check

README.md

@@ -152,6 +152,13 @@ npx jsii-release-nuget [DIR]
 |Option|Required|Description|
 |------|--------|-----------|
 |`NUGET_API_KEY`|Required|[NuGet API Key](https://www.nuget.org/account/apikeys) with "Push" permissions|
+|`NUGET_SERVER`|Optional|NuGet Server URL (defaults to nuget.org)|
+
+**Publish to GitHub Packages**
+
+* Set `NUGET_SERVER` to `https://nuget.pkg.github.com/(`org or user`).
+* Set `NUGET_API_KEY` to a token with write packages permissions.
+* Make sure the repository url in the project file matches the org or user used for the server 
 
 ## PyPI
 
@@ -177,7 +184,7 @@ npx jsii-release-pypi [DIR]
 ## Roadmap
 
 - [X] GitHub Support: Maven
-- [ ] GitHub Support: NuGet
+- [X] GitHub Support: NuGet
 - [ ] CodeArtifact Support: Maven
 - [ ] CodeArtifact Support: NuGet
 - [ ] CodeArtifact Support: Python

bin/jsii-release-nuget

@@ -29,7 +29,7 @@ fi
 
 echo "Publishing NuGet packages..."
 
-nuget_source="https://api.nuget.org/v3/index.json"
+nuget_source="${NUGET_SERVER:-"https://api.nuget.org/v3/index.json"}"
 nuget_symbol_source="https://nuget.smbsrc.net/"
 
 log=$(mktemp -d)/log.txt
@@ -50,7 +50,7 @@ for package_dir in ${packages}; do
         # If push failed, check if this was caused because we are trying to publish
         # the same version again, which is not an error by searching for a magic string in the log
         # ugly, yes!
-        if cat ${log} | grep -q "already exists and cannot be modified"; then
+        if cat ${log} | grep -q -e "already exists and cannot be modified" -e "409 (Conflict)"; then
             echo "⚠️ Artifact already published. Skipping"
         elif [ "${exit_code}" -ne 0 ]; then
             echo "❌ Release failed"