Mark the avro extensions as "stable"

[edeandrea]

Currently the quarkus-avro, quarkus-apicurio-registry-avro, and quarkus-confluent-registry-avro extensions are shown as experimental. This PR moves them to stable.

[quarkus-bot]

Failing Jobs - Building 8100f33

Status	Name	Step	Failures	Logs	Raw logs
✔️	Gradle Tests - JDK 11
✖	Gradle Tests - JDK 11 Windows	Build	Failures	Logs	Raw logs

Full information is available in the Build summary check run.

Failures

⚙️ Gradle Tests - JDK 11 Windows #

- Failing: integration-tests/gradle 

📦 integration-tests/gradle

✖ io.quarkus.gradle.devmode.KotlinProjectWithCompilerArgsDevModeTest.main line 17 - More details - Source on GitHub

org.awaitility.core.ConditionTimeoutException: Condition with lambda expression in io.quarkus.test.devmode.util.DevModeTestUtils that uses java.util.function.Supplier, java.util.function.Supplierjava.util.concurrent.atomic.AtomicReference, java.util.concurrent.atomic.AtomicReferencejava.lang.String, java.lang.Stringboolean was not fulfilled within 2 minutes.
	at org.awaitility.core.ConditionAwaiter.await(ConditionAwaiter.java:167)
	at org.awaitility.core.CallableCondition.await(CallableCondition.java:78)

[juniormichieletto]

Awesome @edeandrea! Thank you so much :D