security: spring-security-oauth2 is not an optional dependency but should be

[kaibra]

v1.2.27 introduced an optional dependency to org.springframework.security.oauth:spring-security-oauth2 in the security starter.
But the implementation is not optional. It causes ClassNotFoundExceptions when the dependency is not provided:

Caused by: java.lang.ClassNotFoundException: org.springframework.security.oauth2.provider.endpoint.FrameworkEndpointHandlerMapping
at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:583) ~[na:na]
at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:178) ~[na:na]
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:521) ~[na:na]
... 62 common frames omitted

Cause is https://github.com/springdoc/springdoc-openapi/blob/master/springdoc-openapi-security/src/main/java/org/springdoc/core/SpringDocSecurityConfiguration.java#L29

@ConditionalOnBean(FrameworkEndpointHandlerMapping.class) does not work like this if the Bean itself is injected within the same signature.