Fixed error with indexed params

Author: mishamyte

src/Serilog.Sinks.Grafana.Loki/LokiBatchFormatter.cs

@@ -160,7 +160,7 @@ private Dictionary<string, string> GenerateLabels(LogEvent logEvent)
                 // to turn them into valid label keys and at the same time denote them as ordinal parameters.
                 if (char.IsDigit(key[0]))
                 {
-                    key = $"Param-{key}";
+                    key = $"param{key}";
                 }
 
                 // Some enrichers generates extra quotes and it breaks the payload

test/Serilog.Sinks.Grafana.Loki.Tests/IntegrationTests/Approvals/RequestPayloadTests.LabelsForIndexedPlaceholdersShouldBeCreatedWithParamPrefix.approved.txt

@@ -1 +1 @@
-{"streams":[{"stream":{"Param-0":"Namespace.Module.Method"},"values":[["<unixepochinnanoseconds>","An error occured in \u0022Namespace.Module.Method\u0022"]]}]}
+{"streams":[{"stream":{"param0":"Namespace.Module.Method"},"values":[["<unixepochinnanoseconds>","An error occured in \u0022Namespace.Module.Method\u0022"]]}]}