Follow-up to https://github.com/sourcegraph/sourcegraph/pull/44034

Done

Ensure the following works,

• Skippable steps
  • Dynamic skipping (e.g. output of previous step determines if step should be skipped)
  • Hard coded skip
• Workspace File Mounts
  • Binary
  • Script
  • Sub-directory
• File Mounts
  • It is unclear if all variants of file mounts still work. Basic cases do work. Files used to be read-only in src-cli, they aren't now, but content is still reset in between steps.
  • The assumption that everything operates in /data is broken here, because we need to use what executors give us to persist out-of-repo state in between containers (like the step result from the previous step)
• tee dependency
  • It depends on tee being available in the docker images to capture the cmd.stdout/cmd.stderr properly for template variable rendering
  • Called out in documentation
• Environment Variable Rendering
  • Env-vars are not rendered in their evaluated form post-execution
• Secrets
• File Permissions
  • File permissions are unclear and might be similarly broken to how they are now - or even worse
• Caching
  • Cache keys are not correctly computed if using workspace mounts - the metadataretriever is nil
• Log Outputs
  • We still use log outputs to transfer the AfterStepResults to the Sourcegraph instance, this should finally become an artifact instead. Then, we don't have to rely on the execution_log_entires anymore and can theoretically prune those after some time. This column is currently growing indefinitely.
  • Created #50538 to track this work.