Ruby: Add Ruby stack for GitLab

[joao10lima]

Context

According to the State of Developer Ecosystem 2021 survey by JetBrains, GitLab CI is the third most used CI system:
https://www.jetbrains.com/lp/devecosystem-2021/team-tools/#Which-Continuous-Integration-CI-systems-do-you-regularly-use

Following the Pipelinit roadmap to expand its supported platforms is necessary an implementation of all the current stacks on the GitLab platform.

Goal

Add Ruby stack for GitLab platform

Implementation

GitLab organizes its CI on different way from GitHub, first it uses a central file called .gitlab-ci.yml and other CIs must be linked to him.

• Adapt the current GitHub implementation to the GitLab format:
  • Create template for the following stages (see this example):
    • lint.yaml
    • format.yaml
  • Then create an .gitlab-ci.yml and link those files in the include field as this example.

Reference:

• https://docs.gitlab.com/ee/ci/jobs/
• https://docs.gitlab.com/ee/ci/yaml/
• https://docs.gitlab.com/ee/ci/yaml/#include

To test

• Create a free account on https://gitlab.com/
• Create a new repository and push an Ruby project that you want to test Pipelinit
• Push a commit to a branch and then open a Pull request with changes following the stack you're working.

Obs: You can check if the pipeline is correct before a commit using the tool https://pypi.org/project/gitlab-lint/ , install it with python3 -m pip install -g gitlab_lint