Remove project name support in v2

[batsatt]

We currently have support for two different "names" with identical default values in the user config:

default.project.name=${init_archetype}-${init_flavor}
default.artifact.id=${init_archetype}-${init_flavor}

The project name is only important for the generated directory name.

The issue is that when in interactive mode with helidon init, it is easy to change one value and not the other, resulting in behavior that violates the principle of least surprise. For example, using "foo" as the project name and accepting the default for artifact id will create a directory name "foo" but the artifact id, jar name, docker image name, etc. will all be based on the default.

Removing support for project name is the cleanest way of avoiding this issue:

1. Use the artifactId value for the directory name
2. Add a warning if --name is supplied saying that it will be unused
3. Add a comment in the generated user config saying that default.project.name is only used for v1

Note that artifactId will now be required and an exception will be thrown if there is no valid value for it.
It will replace the statement below inside ArchetypeEngineV2.

        String projectName = requireNonNull(context.lookup(PROJECT_NAME), "project name is null").asString();

[batsatt]

ArchetypeEngineV2.generate() must be updated to use artifactId for the output directory.
IntegrationTestMojo.processIntegrationTest() must be updated to stop adding the name.