Allow images and services to override pull policy

Problem to solve

This issue would resolve the following problems.

1. The limitations posed by the current pull policy settings. Explained [here](https://docs.gitlab.com/runner/executors/docker.html#how-pull-1. policies-work).
2. This feature allows us to shorten build times by not pulling images when they are already present. In cases we do want to pull images we can either use the default policy (always) or explicitly state we want to always pull an image if the default policy has been changed.
3. We can avoid the security issues raised by using if-not-present by using the policy only when necessary.

Intended users

• Sidney (Systems Administrator)
• Sasha (Software Developer)
• Devon (DevOps Engineer)

Further details

Proposal

Sydney picks a default pull policy based on the needs of the company as a whole. Both Devon and Sasha can alter the pull-policy for services and images in the gitlab-ci.yml file for their respective projects.

Permissions and Security

Unknown.

Documentation

Unknown.

Testing

Unknown.

What does success look like, and how can we measure that?

Boths Sasha and Devon can select an appropriate pull_policy based on the needs of a project.

What is the type of buyer?

Unknown.

Links / references