artifacts support for gitlab-runner exec

Description

To test gitlab pipeline scripts, I use gitlab-runner exec docker in local environment. There are some difficulty about

• cache
• artifacts

Verifying and investigating generated artifacts after job succeed are difficult. To do that I need to setup docker volume according to artifact's path and I need to clean them before run job. It needs unnecessary script to make it easy for each jobs.

Proposal

I think it's better to have the way specify where or how the artifacts are stored.

$ gitlab-runner exec docker build --artifact-outout=./artifact

or

is could be good to have specify where the artifacts are sotred like cache in the docker container.

$ gitlab-runner exec docker build --artifacts-path=/artifact