feat: add TaxCalculator interface for configurable tax calculation

Author: otaviojava

cdi-api/src/main/java/com/otavio/jakarta/cdi/app/configuration/TaxCalculator.java

@@ -0,0 +1,8 @@
+package com.otavio.jakarta.cdi.app.configuration;
+
+import java.math.BigDecimal;
+
+public interface TaxCalculator {
+
+    BigDecimal calculate(BigDecimal amount);
+}