Move backup and restore GitLab page info

What does this MR do?

Reorganize and move some information in the Back up and restore GitLab page to improve the content structure and to meet CTRT guidelines.

Changes in this MR

• Set the main back up and restore page as an overview page with links to more detailed info.
• Created a new page for the backup archive creation process.
• Updated relative links.

Related issues and MRs

• FY25Q3 TW OKR: Refactor high visibility pages f... (technical-writing#1075)
• TW OKR: Review and refactor backup and restore ... (!161904 - merged)

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Link to spreadsheet: CTRT OKR