Rework sample JPA IT using CXF client, JSONB impl rather than MST

[scottkurz]

Rework JPA sample IT to follow pattern in: https://openliberty.io/guides/rest-intro.html#testing-the-service for providing RESTClient & JSONB .. either yasson as shown, or, I think Jackson is more widely used so might be better.

        <dependency>
            <groupId>org.apache.cxf</groupId>
            <artifactId>cxf-rt-rs-client</artifactId>
            <version>3.3.6</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.apache.cxf</groupId>
            <artifactId>cxf-rt-rs-extension-providers</artifactId>
            <version>3.3.6</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.eclipse</groupId>
            <artifactId>yasson</artifactId>
            <version>1.0.7</version>
            <scope>test</scope>
        </dependency>

[scottkurz]

Fixed by OpenLiberty/application-stack-samples#17