fix: properly report imagerunner startup errors

[alexplischke]

Proposed changes

Ensure that imagerunner startup errors are properly reported back to the user.

Here is an example of launching with invalid image pull credentials before this PR:

❯ saucectl run
Running version 0.0.0+unknown
07:55:40 WRN A new version of saucectl is available (v0.164.0)
07:55:40 INF Launching workers. concurrency=2
07:55:40 INF Starting suite. image=europe-west3-docker.pkg.dev/sauce-hto-p-jy6b/abn-amro-sauce/saucelabs-wiremock-dynamic-instance:latest suite="Testing Image Credentials"

       Name                              Duration    Status    Attempts
─────────────────────────────────────────────────────────────────────────
  ✖    Testing Image Credentials               1s                     1
─────────────────────────────────────────────────────────────────────────
  *    All suites have launched                1s
  *

Same example as above, but after the changes:

❯ saucectl run -c .sauce/bad_config.yml
Running version 0.0.0+unknown
10:31:49 WRN A new version of saucectl is available (v0.164.0)
10:31:49 INF Launching workers. concurrency=2
10:31:49 INF Starting suite. image=europe-west3-docker.pkg.dev/sauce-hto-p-jy6b/abn-amro-sauce/saucelabs-wiremock-dynamic-instance:latest suite="Testing Image Credentials"
10:31:50 ERR Suite failed. error="runner start (422): ERR_IMAGE_NOT_ACCESSIBLE: the provided image does not meet the requirements" passed=false runID= suite="Testing Image Credentials"

       Name                                Duration    Status    Attempts
───────────────────────────────────────────────────────────────────────────
  ✖    Testing Image Credentials                 1s    Failed           1
───────────────────────────────────────────────────────────────────────────
  ✖    1 of 1 suites have failed (100%)          1s