Allow triggering the prepare-release workflow manually for Quarkiverse extensions

[gastaldi]

This allows you to retry failed releases without the need to revert changes to .github/project.yml

[quarkus-bot]

Status for workflow Quarkus CI

This is the status report for running Quarkus CI on commit bbd7d51.

✅ The latest workflow run for the pull request has completed successfully.

It should be safe to merge provided you have a look at the other checks in the summary.

You can consult the Develocity build scans.

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Flaky tests - Develocity

⚙️ JVM Tests - JDK 21

📦 extensions/smallrye-reactive-messaging/deployment

✖ io.quarkus.smallrye.reactivemessaging.hotreload.ConnectorChangeTest.testUpdatingConnector - History

• Expecting actual: ["-4","-5","-6","-7","-8","-9","-10","-11"] to start with: ["-3", "-4", "-5", "-6"] - java.lang.AssertionError

java.lang.AssertionError: 

Expecting actual:
  ["-4","-5","-6","-7","-8","-9","-10","-11"]
to start with:
  ["-3", "-4", "-5", "-6"]

	at io.quarkus.smallrye.reactivemessaging.hotreload.ConnectorChangeTest.testUpdatingConnector(ConnectorChangeTest.java:36)

[gsmet]

Indeed, that's a good idea.