Add files for db partition types

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• Link to the merge request that introduced the new page: Resolve "Add documentation for range int pariti... (gitlab!139805 - merged)
• Give the MR a descriptive title.
• Optional. Link to the review app showing the new page existing pages already on the site:
  • https://docs.gitlab.com/ee/development/database/partitioning/
    • https://docs.gitlab.com/ee/development/database/partitioning/date_range.html
    • https://docs.gitlab.com/ee/development/database/partitioning/hash.html
    • https://docs.gitlab.com/ee/development/database/partitioning/int_range.html
    • https://docs.gitlab.com/ee/development/database/partitioning/list.html

Related links

• Related to Add documentation for range int paritioning (gitlab#425721 - closed)
• Related to Resolve "Add documentation for range int pariti... (gitlab!142532 - merged)