[CLI] Improvements for meta and list command

Created by: jmini

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh and ./bin/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\.
• Filed the PR against the correct branch: master, 3.3.x, 4.0.x. Default: master.
• Copied the technical committee to review the pull request if your PR is targeting a particular programming language.

Description of the PR

To reproduce:

Create a my-codegen-openapi-generator artefact using the meta command as described here: https://github.com/OpenAPITools/openapi-generator/blob/master/docs/customization.md#creating-a-new-template

Change 1/: If you create a generator that have no type (CLIENT, SERVER, DOCUMENTATION, CONFIG, OTHER) it should be displayed when you run the command:

(classpath in the windows format, for linux or Mac replace the ; with a :)

java -cp out/generators/my-codegen/target/my-codegen-openapi-generator-1.0.0.jar;modules/openapi-generator-cli/target/openapi-generator-cli.jar org.openapitools.codegen.OpenAPIGenerator

The change introduces the category UNDIFINED for this case. It also skip a category if not generator is present for it.

Change 2/: the meta command is now from type OTHER:

Example MyCodegenGenerator:

  public CodegenType getTag() {
    return CodegenType.OTHER;
  }

Change 3/: meta script is added to ensure-up-to-date