Add generator cli to docker-compose stack

Created by: nilox94

This is mainly for the development process, otherwise you can use the generator from the official docker image. The usage of the script run-in-docker.sh can be done via docker-compose.

docker-compose run generator mvn package
docker-compose run generator generate \
            -i modules/openapi-generator/src/test/resources/2_0/petstore.yaml \
            -g typescript-server \
            -o /openapi-generator/out

Additionally, there is some permission management so that generated projects can have appropriate permissions and also maven repository directory can be written.

PR checklist

• Read the contribution guidelines.
• If contributing template-only or documentation-only changes which will change sample output, build the project before.
• Run the shell script(s) under ./bin/ (or Windows batch scripts under.\bin\windows) to update Petstore samples related to your fix. This is important, as CI jobs will verify all generator outputs of your HEAD commit, and these must match the expectations made by your contribution. You only need to run ./bin/{LANG}-petstore.sh, ./bin/openapi3/{LANG}-petstore.sh if updating the code or mustache templates for a language ({LANG}) (e.g. php, ruby, python, etc).
• File the PR against the correct branch: master, 4.3.x, 5.0.x. Default: master.
• Copy the technical committee to review the pull request if your PR is targeting a particular programming language.