Add integration tests for schema-based multitenancy

[yrodiere]

This does not fix anything, it just adds integration tests (which pass, fortunately). I had to write them while I was working on #15602 , because we didn't have any schema-based multitenancy tests...

[quarkus-bot]

Failing Jobs - Building 290a3a1

Status	Name	Step	Test failures	Logs	Raw logs
✖	JVM Tests - JDK 11	Build	Test failures	Logs	Raw logs
✔️	JVM Tests - JDK 16

Full information is available in the Build summary check run.

Test Failures

⚙️ JVM Tests - JDK 11 #

📦 extensions/arc/deployment

✖ io.quarkus.arc.test.config.ConfigPropertiesTest. - More details - Source on GitHub

java.lang.RuntimeException: org.junit.jupiter.api.extension.TestInstantiationException: Failed to create test instance
	at io.quarkus.test.QuarkusUnitTest.beforeAll(QuarkusUnitTest.java:550)
	at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.lambda$invokeBeforeAllCallbacks$8(ClassBasedTestDescriptor.java:368)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.invokeBeforeAllCallbacks(ClassBasedTestDescriptor.java:368)
	at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.before(ClassBasedTestDescriptor.java:192)
	at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.before(ClassBasedTestDescriptor.java:78)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:136)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org...