Add ParameterProvider.

Change-Id: Iae30648eb41761831840de0ce5617072e69928a4
diff --git a/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/ParameterProvider.java b/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/ParameterProvider.java
new file mode 100644
index 0000000..fb212a3
--- /dev/null
+++ b/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/ParameterProvider.java
@@ -0,0 +1,12 @@
+package eu.mulk.quarkus.googlecloud.jsonlogging;
+
+/**
+ * A user-supplied provider for {@link StructuredParameter}s.
+ *
+ * <p>Any CDI beans registered under this class are applied to each log entry that is logged.
+ */
+public interface ParameterProvider {
+
+  /** Provides a {@link StructuredParameter} to add to each log entry that is logged. */
+  StructuredParameter get();
+}