Partially fixes #13629

• Shows/hides Backup screen menu item based on Jetpack capabilities
• Extracts related logic into the JetpackCapabilitiesUseCase

To test:

1. BackupScreenFeatureFlag = false, ScanScreenFeatureFlag = false, MySiteImprovementsFeatureFlag = false
2. Verify both Backup and Scan menu items are hidden for all types of sites

1. BackupScreenFeatureFlag = true, ScanScreenFeatureFlag = false, MySiteImprovementsFeatureFlag = false
2. Verify Backup menu item is shown when the site has BACKUP/BACKUP_DAILY/BACKUP_REALTIME capability and it is not shown when it doesn't have any of the backup capabilities

1. BackupScreenFeatureFlag = false, ScanScreenFeatureFlag = true, MySiteImprovementsFeatureFlag = false
2. Verify Scan menu item is shown when the site has SCAN capability and it is not shown when it doesn't have it

1. BackupScreenFeatureFlag = true, ScanScreenFeatureFlag = false, MySiteImprovementsFeatureFlag = true
2. Verify Backup menu item is shown when the site has BACKUP/BACKUP_DAILY/BACKUP_REALTIME capability and it is not shown when it doesn't have any of the backup capabilities

1. BackupScreenFeatureFlag = false, ScanScreenFeatureFlag = true, MySiteImprovementsFeatureFlag = true
2. Verify Scan menu item is shown when the site has SCAN capability and it is not shown when it doesn't have it

PR submission checklist:

• I have considered adding unit tests where possible.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.