Complains about missing `<extensions>true</extensions>` for newly created extension

[rsvoboda]

Describe the bug

When I build newly created extension I see

[WARNING] The Maven extensions for the Quarkus Maven plugin are not enabled for this build. We recommend enabling this, so that the plugin can verify essential build settings have been configured as required. Please enable by adding "<extensions>true</extensions>" in your quarkus-maven-plugin declaration; it should look like:

	<plugin>
		<groupId>${quarkus.platform.group-id}</groupId>
		<artifactId>quarkus-maven-plugin</artifactId>
		<version>${quarkus.platform.version}</version>
		<extensions>true</extensions> <!-- THIS ONE -->
		...

This is happens for 2 modules: Documentation and Integration Tests

Naive solution would be to add the line to the template for the root pom.xml file of the generated extension
That would be https://github.com/quarkusio/quarkus/blob/main/independent-projects/tools/base-codestarts/src/main/resources/codestarts/quarkus-extension/code/extension-base/java/pom.tpl.qute.xml#L78

I'm not sure if it's intentional to skip <extensions>true</extensions> for extensions.
CC @gsmet / @aloubyansky

Expected behavior

Experience with no warnings

Actual behavior

Warnings are present

How to Reproduce?

Reproducer:

quarkus create extension extension-abc
cd quarkus-extension-abc
mvn clean verify

Output of uname -a or ver

macOS

Output of java -version

21

Quarkus version or git rev

3.34.3 and main

Build tool (ie. output of mvnw --version or gradlew --version)

No response

Additional information

No response

[gsmet]

This is unfortunately a topic that is more complex than it seems:

• for extensions added to the core repo: we can't have <extensions>true</extensions> because otherwise the first build will fail as you need the extension available before the build can even start
• for all extensions outside of the core repo: we should add it

I think we already make a difference between the two so it's doable.

[rsvoboda]

This is unfortunately a topic that is more complex than it seems:

Yeah, I thought so :). That's why I created this issue instead of a PR for the naive way I described above.