Add warning for snapshot docs

If the project version is a SNAPSHOT a warning
is added at the top of the docs stating this fact.

spring-pulsar-docs/spring-pulsar-docs.gradle

@@ -92,7 +92,8 @@ tasks.withType(org.asciidoctor.gradle.jvm.AbstractAsciidoctorTask) {
 				"spring-pulsar-binder-version": project.springPulsarBinderVersion ?: 'current',
 				"spring-pulsar-starter-version": project.springPulsarStarterVersion ?: 'current',
 				"pulsar-client-version": project.pulsarClientVersion ?: 'current',
-				"pulsar-client-reactive-version": project.pulsarClientReactiveVersion ?: 'current'
+				"pulsar-client-reactive-version": project.pulsarClientReactiveVersion ?: 'current',
+				"is-snapshot-version": project.version.endsWith("-SNAPSHOT")
 	}
 }
 

spring-pulsar-docs/src/main/asciidoc/attributes-variables.adoc

@@ -6,6 +6,7 @@
 :spring-pulsar-starter-version: current
 :pulsar-client-version: current
 :pulsar-client-reactive-version: current
+:is-snapshot-version:  false
 
 :github: https://github.com/spring-projects/spring-pulsar
 :javadocs: https://docs.spring.io/spring-pulsar/docs/{spring-pulsar-version}/api

spring-pulsar-docs/src/main/asciidoc/index.adoc

@@ -7,6 +7,10 @@ include::authors.adoc[]
 
 include::copyright.adoc[]
 
+ifeval::[{is-snapshot-version} == true]
+CAUTION: You are viewing documentation for a SNAPSHOT version ({spring-pulsar-version}). While it is usually in-sync with the underlying code, it is subject to change and not guaranteed to be up-to-date with the underlying code.
+endif::[]
+
 include::intro.adoc[leveloffset=+1]
 
 include::getting-help.adoc[leveloffset=+2]