[dynamic control] Add PolicyTypeInitializer interface for better readability (#2754)

Author: jackshirazi

dynamic-control/src/main/java/io/opentelemetry/contrib/dynamic/policy/PolicyTypeInitializer.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.contrib.dynamic.policy;
+
+import io.opentelemetry.sdk.autoconfigure.spi.AutoConfigurationCustomizer;
+import javax.annotation.Nonnull;
+
+/**
+ * NOTE PolicyInit not yet added - remove this note when it is added
+ *
+ * <p>Initializes one policy type and returns the implementer that applies that type at runtime.
+ *
+ * <p>This is used by {@code
+ * io.opentelemetry.contrib.dynamic.policy.registry.PolicyInit.registerPolicyType(...)} and is
+ * typically provided as a method reference, for example:
+ *
+ * <pre>{@code
+ * io.opentelemetry.contrib.dynamic.policy.registry.PolicyInit.registerPolicyType(
+ *     TraceSamplingRatePolicy.POLICY_TYPE,
+ *     TraceSamplingRatePolicy.class,
+ *     TraceSamplingRatePolicy::initialize);
+ * }</pre>
+ */
+@FunctionalInterface
+public interface PolicyTypeInitializer {
+  /**
+   * Initializes policy runtime wiring for one policy type.
+   *
+   * @param autoConfiguration OpenTelemetry auto-configuration customizer
+   * @return non-null implementer for the policy type
+   */
+  @Nonnull
+  PolicyImplementer initialize(AutoConfigurationCustomizer autoConfiguration);
+}