Refactor Playwright auth steps into separate CI step so the shards do not repeat setup

[grahamlangford]

Motivation

• We introduced sharding to dramatically reduce the Playwright runtime but each shard has to run authentication
• Running the authentication once in a separate step that the Playwright shards inherit would further reduce the time needed to run tests

Acceptance Criteria

• GitHub Actions that run Playwright tests all run an auth step as a prerequisite to the tests running

[github-actions]

This issue will be closed in 7 days unless the stale label is removed, or a comment is added to the issue.

[grahamlangford]

Duplicate of #8912