Draft: Update stages.yml to add application_performance category to Cloud Connector group

First change to address gitlab-org/gitlab!133238 (comment 1590104107)

Approvals

Merge requests with changes to stages and groups and significant changes to categories need to be created, approved, and/or merged by each of the below:

See approvals in related issue: #34461

The following people need to be on the merge request so they stay informed:

• Vice President of Development @clefelhocz1
• Vice President of Infrastructure & Quality @meks
• Vice President of User Experience @clenneville
• The Product Marketing Manager relevant to the stage group(s)
• Director of Technical Writing @susantacker

After Approvals and Merge

• Create an issue in the triage-ops project to update GitLab Bot automation:
  • for Category change
  • for Stage or Group change
  • If label migration is required, please follow the self-serve instructions to get started on a one-off label migration MR.
• Mention the product group Technical Writer to update the documentation metadata
• Share MR in #product, #development, and relevant #s_, #g_, and #f_ slack channels