Clarify table statistics recreation - Docs

What does this MR do?

Update and clarify step 7 of the Upgrade non-packaged PostgreSQL document, which was awkward and hard to follow. This change should make it clearer.

Related issues

Author's checklist

• Consider taking the GitLab Technical Writing Fundamentals course
• Follow the:
  • Documentation process.
  • Documentation guidelines.
  • Style Guide.
• When ready for review, MR is labeled "~workflow::ready for review" per the Distribution MR workflow

If you are only adding documentation, do not add any of the following labels:

• ~"feature"
• ~"frontend"
• ~"backend"
• ~"bug"
• ~"database"

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

Review 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:
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  • If relevant to this MR, ensure content topic type principles are in use, including:
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    • Any task steps should be written as a numbered list.
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• Ensure a release milestone is set.