Docs: Caution against generating only HTML quality report

What does this MR do?

When you request an HTML report from Code Quality, it omits the JSON report. This breaks essentially all features that need a JSON report.

The first option in the docs today is actually the dangerous one (omits JSON) while the second is the one we should recommend (generates both JSON and HTML). There are downsides to both, and those downsides are now noted in NOTE and WARNING admonitions.

Related issues

gitlab-org/ci-cd/codequality#10 (closed) links to the MRs where the feature is added, including options and tradeoffs

run.sh shows that only one of the formats can be used at once: https://gitlab.com/gitlab-org/ci-cd/codequality/-/blob/3d034b2bed36841431124bab0f2be63a0f7c55cb/run.sh#L124

Customer support issue: https://gitlab.zendesk.com/agent/tickets/289080 (team members only)

Related Slack thread: https://gitlab.slack.com/archives/CLA54H7PY/p1652866295167449 (team members only)

Author's checklist

• Optional. Consider taking the GitLab Technical Writing Fundamentals course.
• Follow the:
  • Documentation process.
  • Documentation guidelines.
  • Style Guide.
• N/A If you're adding or changing the main heading of the page (H1), ensure that the product tier badge is added.
• If you are a GitLab team member, request a review based on:
  • The documentation page's metadata.
  • The associated Technical Writer.

If you are a GitLab team member and only adding documentation, do not add any of the following labels:

• ~"frontend"
• ~"backend"
• ~"type::bug"
• ~"database"

These labels cause the MR to be added to code verification QA issues.

Reviewer's checklist

Documentation-related MRs should be reviewed by a Technical Writer for a non-blocking review, based on Documentation Guidelines and the Style Guide.

• If the content requires it, ensure the information is reviewed by a subject matter expert.
• Technical writer review items:
  • Ensure docs metadata is present and up-to-date.
  • Ensure the appropriate labels are added to this MR.
  • Ensure a release milestone is set.
  • If relevant to this MR, ensure content topic type principles are in use, including:
    • The headings should be something you'd do a Google search for. Instead of Default behavior, say something like Default behavior when you close an issue.
    • The headings (other than the page title) should be active. Instead of Configuring GDK, say something like Configure GDK.
    • Any task steps should be written as a numbered list.
    • If the content still needs to be edited for topic types, you can create a follow-up issue with the docs-technical-debt label.
• Review by assigned maintainer, who can always request/require the reviews above. Maintainer's review can occur before or after a technical writer review.