Document all used vendor extensions in specific generator (#11797)

docs/generators/java.md

@@ -84,6 +84,16 @@ These options may be applied as additional-properties (cli) or configOptions (pl
 |useRxJava3|Whether to use the RxJava3 adapter with the retrofit2 library. IMPORTANT: This option has been deprecated.| |false|
 |withXml|whether to include support for application/xml content type and include XML annotations in the model (works with libraries that provide support for JSON and XML)| |false|
 
+## SUPPORTED VENDOR EXTENSIONS
+
+| Extension name | Description | Applicable for | Default value |
+| -------------- | ----------- | -------------- | ------------- |
+|x-discriminator-value|Used with model inheritance to specify value for discriminator that identifies current model|MODEL|
+|x-implements|Ability to specify interfaces that model must implements|MODEL|empty array
+|x-setter-extra-annotation|Custom annotation that can be specified over java setter for specific field|FIELD|When field is array & uniqueItems, then this extension is used to add `@JsonDeserialize(as = LinkedHashSet.class)` over setter, otherwise no value
+|x-webclient-blocking|Specifies if method for specific operation should be blocking or non-blocking(ex: return `Mono<T>/Flux<T>` or `return T/List<T>/Set<T>` & execute `.block()` inside generated method)|OPERATION|false
+
+
 ## IMPORT MAPPING
 
 | Type/Alias | Imports |