Update RealWorld example application

[Joseph-Cass]

Without knowledge of this codebase I implemented the RealWorld specification here: https://github.com/JCass149/openliberty-microprofile-realworld-example-app

There are a lot of similarities between the two implementations, but there are a few parts which my team and I feel will be valuable to port into this application:

• [ ] 1. Upgrade to the latest version of Liberty and MicroProfile. For self-explanatory reasons. Mainly to include liberty:dev mode.
• [ ] 2. Include the mpOpenAPI code from here. To allow users to visualise and interact with the endpoints.
• [ ] 3. Use specialised JPA queries like this one. I think this will fix a bug here where the retrieved data is processed after making a request of max size 20.
• [ ] 4. Include the additional tests from here. The additional tests test things not currently tested in this application.
• [ ] 5. Update the readme respective to the above changes. In particular how to use liberty:dev mode and openapi/ui.

[appiepollo14]

See my PR, I've implemented mostly the thinks you've asked. Once merged I can look into the mpOpenApi specs.