improve: add license headers to source files #5671

Job	Run time
sample_operators_tests (sample-operators/mysql-schema)	3m 37s
sample_operators_tests (sample-operators/tomcat-operator)	3m 43s
sample_operators_tests (sample-operators/webpage)	4m 8s
sample_operators_tests (sample-operators/leader-election)	4m 15s
	15m 43s

Provide feedback