Add integration tests for MessageResource

[mcruzdev]

Test conventions

• We must use assertj library
• The test naming must be should_expectedBehavior_when_stateUnderTest example: should_throwException_when_ageLessThan18.

We can get as example the https://github.com/quarkiverse/quarkus-flow repository that contains integration tests using a LLM locally.

[Gabrielx47]

@mcruzdev I want to work on this issue.

[mcruzdev]

Assigned @Gabrielx47, thanks!

[Gabrielx47]

Okay, @mcruzdev . Thank you.