Fix Ignite 3 build and publishing for beta 1

Need to make a few small fixes in the build and publishing process:

• Fix the readme to mention beta 1 instead of alpha 5
• Automatically build and sign src.zip
• Automatically build and sign .NET NuGet package (package .nuget into a .nuget.zip like it is done in 2.x)
• Update release.md as needed

The following artifacts need to be uploaded to the release repository:

• src.zip
• ignite: zip, rpm, deb
• ignite-db: zip, rpm, deb
• ignite-client: jar
• nuget.zip