[docker-up] Auto-login if GITPOD_IMAGE_AUTH is set

[geropl]

Description

So far GITPOD_IMAGE_AUTH had two issues:

• it was not present in the default env in terminals, although it was present in gp env
• it was used for pulling docker images in image builder, but not used in workspaces to authenticated the docker daemon
  This PR fixes both issues.

Related Issue(s)

Fixes CLC-1098

How to test

• join this org
• start a workspace, and note:
  • env | grep GITPOD_IMAGE_AUTH is not empty
  • test gp validate:
    • change first line in .gitpod.yml to image: geropl/workspace-base:latest
    • hit gp validate and note how it successfully pulls the base image

Documentation

Preview status

Gitpod was successfully deployed to your preview environment.

• 🏷️ Name - gpl-1098-dockerup
• 🔗 URL - gpl-1098-dockerup.preview.gitpod-dev.com/workspaces.
• 📚 Documentation - See our internal documentation for information on how to interact with your preview environment.
• 📦 Version - gpl-1098-dockerup-gha.31103
• 🗒️ Logs - GCP Logs Explorer

Build Options

Build

• /werft with-werft
  Run the build with werft instead of GHA
• leeway-no-cache
• /werft no-test
  Run Leeway with --dont-test

Publish

• /werft publish-to-npm
• /werft publish-to-jb-marketplace

Installer

• analytics=segment
• with-dedicated-emulation
• workspace-feature-flags
  Add desired feature flags to the end of the line above, space separated

Preview Environment / Integration Tests

• /werft with-local-preview
  If enabled this will build install/preview
• /werft with-preview
• /werft with-large-vm
• /werft with-gce-vm
  If enabled this will create the environment on GCE infra
• /werft preemptible
  Saves cost. Untick this only if you're really sure you need a non-preemtible machine.
• with-integration-tests=all
  Valid options are all, workspace, webapp, ide, jetbrains, vscode, ssh. If enabled, with-preview and with-large-vm will be enabled.
• with-monitoring

/hold