Improve docker without buildpacks documentation

Explain how CDS can be enabled with plain Dockerfiles.

Closes gh-42106

spring-boot-project/spring-boot-docs/src/docs/antora/modules/reference/partials/dockerfile

@@ -0,0 +1,21 @@
+# Perform the extraction in a separate builder container
+FROM bellsoft/liberica-openjre-debian:17-cds AS builder
+WORKDIR /builder
+# This points to the built jar file in the target folder
+# Adjust this to 'build/libs/*.jar' if you're using Gradle
+ARG JAR_FILE=target/*.jar
+# Copy the jar file to the working directory and rename it to application.jar
+COPY ${JAR_FILE} application.jar
+# Extract the jar file using an efficient layout
+RUN java -Djarmode=tools -jar application.jar extract --layers --destination extracted
+
+# This is the runtime container
+FROM bellsoft/liberica-openjre-debian:17-cds
+WORKDIR /application
+# Copy the extracted jar contents from the builder container into the working directory in the runtime container
+# Every copy step creates a new docker layer
+# This allows docker to only pull the changes it really needs
+COPY --from=builder /builder/extracted/dependencies/ ./
+COPY --from=builder /builder/extracted/spring-boot-loader/ ./
+COPY --from=builder /builder/extracted/snapshot-dependencies/ ./
+COPY --from=builder /builder/extracted/application/ ./