Mark SourceFlow.Cloud.Azure as 2.0.0-beta.1 prerelease

Ship the Azure provider as a prerelease alongside the GA v2.0.0 packages:
core command + event messaging is proven on the Service Bus emulator, while
Key Vault, Managed Identity, subscription SQL-filtering, and real-Azure
behaviour are not yet validated. AssemblyVersion/FileVersion stay 2.0.0.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: NinjaRocks

src/SourceFlow.Cloud.Azure/SourceFlow.Cloud.Azure.csproj

@@ -5,7 +5,7 @@
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
     <LangVersion>latest</LangVersion>
-    <Version>2.0.0</Version>
+    <Version>2.0.0-beta.1</Version>
     <AssemblyVersion>2.0.0</AssemblyVersion>
     <FileVersion>2.0.0</FileVersion>
     <RepositoryUrl>https://github.com/CodeShayk/SourceFlow.Net</RepositoryUrl>