Digital Ocean support (e.g. for students and hobby projects)

[keskiju]

• Add Digital Ocean command line tools to Dockerfile and Dockerfile-ci-do of Taito CLI dependencies and build the new image on Docker Hub.
• Add Dockerfile-ci-do for Taito CLI and build the new cli-dev and ci-do-dev images on Docker Hub.
• Implement do and do-zone plugins for Taito CLI. See aws, aws-zone, gcp and gcp-zone plugins for an example. TIP: checkout dev branch and run local implementations with development mode (-d), e.g. taito -d zone apply.
• Implement terraform module for creating a Digital Ocean zone. Use aws and gcp as an example: https://github.com/TaitoUnited/taito-terraform-modules/tree/master/infrastructure
• Implement do infrastructure template: https://github.com/TaitoUnited/taito-infrastructure/tree/master/templates
• Test it by creating a new project based on full-stack-template: `taito -o my-do project create: full-stack-template)

For now you can use Google Cloud Build for CI/CD and Google Container Registry for storing container images. Or alternatively you can implement support also for GitHub actions (see issue #75) and Docker Registry (see issue #81).

Once you get the Kubernetes cluster running, you can also install EFK (see issue #79).