some server Refactorings and tests with reactive webclient for learning

[lauksas]

Hello!

First, thank you very much for that medium article, it really helped me understanding the security and webflux parts.
I figured to do some jUnit tests to both, automate and learn how to use the reactive web client. Thought on sharing this code so people can also refer to the client part of it. I hope you find this contribution useful.

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Changes sumary :
pom.xml

• updated spring version to latest.
• updated java version to 17
• added spring dependencies to help with development

ResourceREST.java

• added a mapping for the entire class

WebSecurityConfig.java

• refactored in the "reactive form" as warned by IDE using new spring version.

additional-spring-configuration-metadata.json

• will remove warnings from spring IDE and document the properties.

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