Log when downloading, starting analyzers

What does this MR do?

This MR makes logging more precise to improve realtime UX.

Displaying "Starting analyzer..." message before starting to pull the analyzer image (therefore, in adavance to start to create an analyzer container) has generated a long gap typically dozens of seconds to minutes. To prevent this, after finished to pull the image (that is, just before creating a container) "Starting analyzer..." message will come to be displayed. Instead, additonal message "Downloading analyzer" will be displayed when starting to pull the image.

What are the relevant issue numbers?

Part of gitlab-org/gitlab#196159 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added
• [n/a] Documentation created/updated for GitLab EE, if necessary
• [n/a] Documentation created/updated for this project, if necessary
• [n/a] Documentation reviewed by technical writer or follow-up review issue created
• [-] Tests added for this feature/bug; manual test using QA job, see https://gitlab.com/gitlab-org/security-products/tests/php-composer/-/jobs/399345431
• [n/a] Job definition updated, if necessary
  • [n/a] Auto-DevOps template
  • [n/a] Job definition example
  • [n/a] CI Templates
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• [-] Security reports checked/validated by reviewer