Add StreamStatusService class and IStreamGraphBuilder interface

src/Contracts/Annotations.cs

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+namespace Arcane.Framework.Contracts;
+
+/// <summary>
+/// Streaming job annotation keys that can be used by a StreamRunner and a Stream Operator
+/// This class should be removed in future and replaced with Stream-class based contracts, see #23
+/// </summary>
+public class Annotations
+{
+    /// <summary>
+    /// Annotation that signals to StreamOperator to start backfill process
+    /// If the streaming job was marked with this annotation, StreamOperator stops the current stream and starts
+    /// a backfill job.
+    /// </summary>
+    public const string STATE_ANNOTATION_KEY = "arcane.streaming.sneaksanddata.com/state";
+
+    /// <summary>
+    /// Annotation value signals to StreamOperator to start backfill process
+    /// If the streaming job was marked with this annotation, StreamOperator stops the current stream and starts
+    /// a backfill job.
+    /// </summary>
+    public const string SCHEMA_MISMATCH_STATE_ANNOTATION_VALUE = "schema-mismatch";
+}

src/Services/Base/IStreamGraphBuilder.cs

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+using System.Threading.Tasks;
+using Akka.Streams;
+using Akka.Streams.Dsl;
+
+namespace Arcane.Framework.Services.Base;
+
+/// <summary>
+/// Base interface for classes that build Akka.NET stream graphs.
+/// This interface is intended to be implemented by the streaming plugin.
+/// </summary>
+/// <typeparam name="TStreamContext">Type of the StreamContext class</typeparam>
+public interface IStreamGraphBuilder<in TStreamContext> where TStreamContext : IStreamContext
+{
+    /// <summary>
+    /// Build an instance of the runnable Akka.NET graph.
+    /// </summary>
+    /// <param name="context">StreamContext instance.</param>
+    /// <returns>Runnable graph that materialized to a UniqueKillSwitch and a Task.</returns>
+    public IRunnableGraph<(UniqueKillSwitch, Task)> BuildGraph(TStreamContext context);
+}

src/Services/Base/IStreamStatusService.cs

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+using System.Threading.Tasks;
+
+namespace Arcane.Framework.Services.Base;
+
+/// <summary>
+/// A service that allows to report stream status events to the maintainer service.
+/// It can be useful to report a stream status that triggers the maintainer service to take action (schema mismatch, etc.)
+/// </summary>
+public interface IStreamStatusService
+{
+    /// <summary>
+    /// Report that schema mismatch occured to the maintainer service.
+    /// </summary>
+    /// <param name="streamId">Id of the current stream.</param>
+    Task ReportSchemaMismatch(string streamId);
+}
+

src/Services/StreamStatusService.cs

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+using System.Threading.Tasks;
+using Arcane.Framework.Contracts;
+using Arcane.Framework.Services.Base;
+using Snd.Sdk.Kubernetes.Base;
+
+namespace Arcane.Framework.Services;
+
+internal class StreamStatusService: IStreamStatusService
+{
+    private readonly IKubeCluster kubernetesService;
+    public StreamStatusService(IKubeCluster kubernetesService)
+    {
+        this.kubernetesService = kubernetesService;
+    }
+
+    public Task ReportSchemaMismatch(string streamId)
+    {
+        var nameSpace = this.kubernetesService.GetCurrentNamespace();
+        return this.kubernetesService.AnnotateJob(streamId,
+            nameSpace,
+            Annotations.STATE_ANNOTATION_KEY,
+            Annotations.SCHEMA_MISMATCH_STATE_ANNOTATION_VALUE);
+    }
+}