[Java] Add `SuppressWarnings("all")` to all generated Java source files

Is your feature request related to a problem? Please describe.

I'm seeing tons of warnings in the Eclipse IDE for the generated files. Part of these can be resolved by having generators include a SuppressWarnings("all") annotation, but IMHO, all generated sources should always carry this by default.

Describe the solution you'd like

When generating a source file, include this annotation on the class, for all files generated, always and by default.

Describe alternatives you've considered

Configuring the generator, for example for Spring:

                    <configuration>
                        <inputSpec>m2m-connector-contract/openapi.yaml</inputSpec>
                        <generatorName>spring</generatorName>
                        <configOptions>
                            <additionalModelTypeAnnotations>
                                @SuppressWarnings("all")
                            </additionalModelTypeAnnotations>
                            <additionalOneOfTypeAnnotations>
                                @SuppressWarnings("all")
                            </additionalOneOfTypeAnnotations>
                            <additionalEnumTypeAnnotations>
                                @SuppressWarnings("all")
                            </additionalEnumTypeAnnotations>
                        </configOptions>
                    </configuration>

Unfortunately, this doesn't cover the *Api interfaces it generates, nor the ApiUtil class (but that one is warning free).

Start with the Spring generator configuration and the generated *Api interfaces, comparing them with the model, enum, and oneOf annotation options described in the issue. Check how generated Java classes and the ApiUtil class are emitted. Done means every generated Java source file, including *Api interfaces, carries SuppressWarnings("all") by default without requiring additional configuration.