Clean up the Integrations API page

What does this MR do and why?

• Uses consistent heading text:
  • <integration_name>
    • Set up <integration_name>
    • Disable <integration_name>
    • Get <integration_name> settings
• Updates integration names to match those at https://docs.gitlab.com/ee/user/project/integrations/#available-integrations and https://gitlab.com/gitlab-org/gitlab/-/settings/integrations
• Deletes the entries for the following deprecated integrations:
  • Shimo
  • Prometheus
  • jenkins-deprecated
• Fixes the punctuation and formatting in some tables

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Before	After

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