doc: correct documentation to store and retrieve a full body

[dirkbolte]

• provided test case to ensure functionality

References

115

Submitter checklist

• [ ] Recommended: Join WireMock Slack to get any help in #help-contributing or a project-specific channel like #wiremock-java
• [ ] The PR request is well described and justified, including the body and the references
• [ ] The PR title represents the desired changelog entry
• [ ] The repository's code style is followed (see the contributing guide)
• [ ] Test coverage that demonstrates that the change works as expected
• [ ] For new features, there's necessary documentation in this pull request or in a subsequent PR to wiremock.org