Add Risk and Test - Backup Unencrypted [backup-unencrypted]

[e-a-security]

This PR closes #2541.

[cpholguera]

Updated title and linking to issue in description (using the "closes #2541" statement).

[cpholguera]

Thanks for opening the PR @e-a-security! Here's some initial feedback to comply with our structure and guidelines. We'll do a more in-depth tech review after all this is fixed.

• Remove any README.md files you have (you may be able to reuse the info in those files to create the missing test.md and example.md files, see below)
• Add test.md files under each folder:
  • android-backup-unencrypted/test.md
  • ios-backup-unencrypted/test.md - Add example.md files and add number to the example folders:
  • android-backup-unencrypted/example-1/example.md
  • ios-backup-unencrypted/example-1/example.md
• Fix the metadata in risk.md file, see the GitHub issue. This is called "yaml frontmatter" and is used in markdown files to enter metadata. It must follow the provided syntax including those --- delimiters and lowercase keys.
• Rules have some predefined metadata, including a "summary" field which you can use to enter the description of each rule instead of using a README.md file. See one example here

See all guidelines here: https://docs.google.com/document/d/1EMsVdfrDBAu0gmjWAUEs60q-fWaOmDB5oecY9d9pOlg/edit?usp=sharing

At the beginning of that document you can find links to existing risks and tests so you can follow the same structure. If you still have questions after looking into that please let me know.