Update Steps for Running Manual QA Pipeline Against Staging

Why is this change being made?

When following the current steps outlined on the Quality Engineering Tips and Tricks handbook page for generating a pipeline to run an MR's changes against Staging, the pipeline will experience issues authenticating to the registry as raised in this issue: gitlab-org/quality/quality-engineering/team-tasks#1670 (closed)

See gitlab-org/quality/quality-engineering/team-tasks#1670 (comment 1292219565) for more details

This MR adds a step to add the variable GITLAB_QA_CONTAINER_REGISTRY_ACCESS_TOKEN to force using the production gitlab-qa user's access token, rather than the staging gitlab-qa user. This will then allow the tests to authenticate with the registry without overriding GITLAB_QA_ACCESS_TOKEN, which needs the staging gitlab-qa user's token for the tests themselves.

It also updates the staging pipeline link to include additional missing variables.

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