Add doc: how to use custom Kotlin version (Gradle)

I don't know how to do this for Maven, I think I've tried once and it was harder than this
If anyone knows, would be great to add for Maven as well

docs/src/main/asciidoc/kotlin.adoc

@@ -303,7 +303,28 @@ tasks.withType<org.jetbrains.kotlin.gradle.tasks.KotlinCompile> {
 <1> The Kotlin plugin version needs to be specified.
 <2> The all-open configuration required, as per Maven guide above
 
+=== Overriding the Quarkus BOM Kotlin version (Gradle)
 
+If you want to use a different version than the one specified by Quarkus' BOM in your application (for example, to try pre-release features or for compatibility reasons), you can do so by using the `strictly {}` version modifier in your Gradle dependencies. For instance:
+
+[source,kotlin]
+----
+plugins {
+    id("io.quarkus")
+    kotlin("jvm") version "1.7.0-Beta"
+    kotlin("plugin.allopen") version "1.7.0-Beta"
+}
+
+dependencies {
+    listOf("kotlin-stdlib-jdk8", "kotlin-reflect").forEach {
+        implementation("org.jetbrains.kotlin:$it") {
+            version {
+                strictly("1.7.0-Beta")
+            }
+        }
+    }
+}
+----
 
 == Live reload