Add support for multiple GitHub deploy key mappings with GitHub Actions

[TrevorGibson-SR]

Proposed as a solution to #807

When cloning multiple private GitHub repositories with SSH, you can use the deploy key mapping feature of the webfactory/ssh-agent GitHub action to map specific SSH keys to their respective GitHub repositories. This works as intended when cloning in the main GitHub runner environment, but fails to translate over to the industrial_ci docker environment.

Webfactory/ssh-agent specifically calls this out and suggests to copy the ~/.ssh directory and ~/.gitconfig file into the docker container to ensure the mappings are carried over. This change simply adds two new docker mount arguments to import the SSH configuration into the Docker container's build environment.

[mathias-luedtke]

We cannot hardcode Gihub-specific paths.

[mathias-luedtke]

Please try adding .gitconfig here:

industrial_ci/industrial_ci/src/isolation/docker.sh

Line 20 in 26ac131

export DOCKER_CREDENTIALS=${DOCKER_CREDENTIALS-.docker .ssh .subversion}

And why would we mount them rw?
This is not advisable for running CI locally.

[mathias-luedtke]

I think we could just add .gitconfig to

industrial_ci/industrial_ci/src/isolation/docker.sh

Line 20 in 3ed9846

export DOCKER_CREDENTIALS=${DOCKER_CREDENTIALS-.docker .ssh .subversion}

[mathias-luedtke]

I think we could just add .gitconfig to

#844

[mathias-luedtke]

@TrevorGibson-SR: The latest version should copy .gitconfig and .ssh. Is there anythings else needed for multiple SSH keys?