Add missing documentation and enhance test coverage for getting-started-reactive-crud

[jedla97]

Hi, this PR add documentation and additional tests to getting-started-reactive-crud.
As for the documentation whole readme was missing and I wasn't able to find any guide on quarkus.io/ so I wrote some steps for this as I was looking how it's work.
The test only included 2 things (get all and delete). I added coverage for testing add and update fruit as it can be useful for people who are looking how to send these request.

Check list:

Your pull request:

• targets the development branch
• uses the 999-SNAPSHOT version of Quarkus
• has tests (mvn clean test)
• works in native (mvn clean package -Pnative)
• has integration/native tests (mvn clean verify -Pnative)
• makes sure the associated guide must not be updated
• links the guide update pull request (if needed)
• updates or creates the README.md file (with build and run instructions)
• for new quickstart, is located in the directory component-quickstart
• for new quickstart, is added to the root pom.xml and README.md

[gsmet]

Thanks. I added a small comment.

Also, probably a good idea for @DavideD to have a look.

[gsmet]

Don't we have a guide for that?

Because we usually avoid duplicating content in the quickstarts. Some of them have a README with a link to the guide.

[jedla97]

I wasn't able to find it so I write at least what it's does. Now after some digging I found out that the guide was there in past but was changed by this PR . It seems that PR replace this quickstart by hibernate-reactive-panache-quickstart.