New: Index on Log table

coscine/issues#2284

MR to master is intended. Has to be released swiftly.

src/Migrations/Migrations/Migration202211040919LogDbIndex.cs

+using FluentMigrator;
+
+namespace Coscine.Migrations.Migrations
+{
+    //yyyymmddhhmm
+    [Migration(202211040919)]
+    public class Migration202211040919LogDbIndex : Migration
+    {
+        public override void Down()
+        {
+            Delete.Index("log_idx_userid_loglevel_servertime").OnTable("Log");
+        }
+
+        public override void Up()
+        {
+            Create.Index("log_idx_userid_loglevel_servertime").OnTable("Log")
+                .OnColumn("UserId").Ascending()
+                .OnColumn("LogLevel").Ascending()
+                .OnColumn("ServerTimestamp").Ascending();
+        }
+    }
+}
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