feat(core): use NOT_NULL serialization in plugins

[loicmathieu]

May be related to #7406

[codecov]

❌ 1 Tests Failed:

Tests completed	Failed	Passed	Skipped
1644	1	1643	6

View the top 1 failed test(s) by shortest run time

io.kestra.runner.mysql.MysqlRunnerRetryTest retryFailedFlowDuration(Execution)

Stack Traces | 5.82s run time

java.lang.AssertionError: 
Expected: is <3>
     but: was <2>
	at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:20)
	at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:6)
	at io.kestra.plugin.core.flow.RetryCaseTest.retryFailedFlowDuration(RetryCaseTest.java:196)
	at io.kestra.jdbc.runner.JdbcRunnerRetryTest.retryFailedFlowDuration(JdbcRunnerRetryTest.java:96)
	at java.base/java.lang.reflect.Method.invoke(Method.java:580)
	at io.micronaut.test.extensions.junit5.MicronautJunit5Extension$2.proceed(MicronautJunit5Extension.java:142)
	at io.micronaut.test.extensions.AbstractMicronautExtension.interceptEach(AbstractMicronautExtension.java:162)
	at io.micronaut.test.extensions.AbstractMicronautExtension.interceptTest(AbstractMicronautExtension.java:119)
	at io.micronaut.test.extensions.junit5.MicronautJunit5Extension.interceptTestMethod(MicronautJunit5Extension.java:129)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)

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