Added ConditionalOnMissingBean to AutoConfiguration

[trimoq]

Fixes #2411.

Add ConditionalOnMissingBean to AxonServerActuatorAutoConfiguration methods to allow users to add AxonServerHealthIndicator and AxonServerStatusAggregator beans more easily, e.g. from third-party libraries.

[smcvb]

Although fair, I'd expect a test case to validate that by defining your own AxonServerHealthIndicator and AxonServerStatusAggregator, you don't receive the defaults from this auto-configuration class. You can check the AxonServerActuatorAutoConfigurationTest to see what such a test would look like.

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
1 Code Smell

100.0% Coverage
0.0% Duplication

[smcvb]

The tests look good, but we need to discuss the conditional statement based on the SimpleStatusAggregator.

[smcvb]

After a short investigation and discussion on the specifics of StatusAggregator instances, we're confident that only a single instance may exist within an application. As such, annotating it with ConditionalOnMissing(SimpleStatusAggregator) should be fine.