Add persistence and replay for failed error imports

Introduces a new persistence mechanism for error messages that failed during their initial ingestion into ServiceControl. This ensures that these messages are reliably stored and can be re-processed at a later time.

The new `FailedErrorImports` table stores the failed messages, including their headers, body, and exception information. A deduplication mechanism ensures that repeated failures of the same message only update the existing record with the latest details.

Author: johnsimons

src/ServiceControl.Persistence.EFCore.PostgreSql/Migrations/20260727055109_AddFailedErrorImports.Designer.cs

@@ -0,0 +1,44 @@
+using System;
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace ServiceControl.Persistence.EFCore.PostgreSql.Migrations
+{
+    /// <inheritdoc />
+    public partial class AddFailedErrorImports : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.CreateTable(
+                name: "failed_error_imports",
+                columns: table => new
+                {
+                    unique_message_id = table.Column<Guid>(type: "uuid", nullable: false),
+                    failed_at = table.Column<DateTime>(type: "timestamp with time zone", nullable: false),
+                    message_id = table.Column<string>(type: "character varying(450)", maxLength: 450, nullable: false),
+                    headers_json = table.Column<string>(type: "text", nullable: false),
+                    body = table.Column<byte[]>(type: "bytea", nullable: false),
+                    body_stored_externally = table.Column<bool>(type: "boolean", nullable: false),
+                    exception_info = table.Column<string>(type: "text", nullable: false)
+                },
+                constraints: table =>
+                {
+                    table.PrimaryKey("pk_failed_error_imports", x => x.unique_message_id);
+                });
+
+            migrationBuilder.CreateIndex(
+                name: "ix_failed_error_imports_failed_at",
+                table: "failed_error_imports",
+                column: "failed_at");
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropTable(
+                name: "failed_error_imports");
+        }
+    }
+}