Change automated backup mode, resolves #304

[NJahreis]

🔀 Purpose of this PR:

• Improves or enhances existing features: Use settings for automated backups instead of general backup base settings
• Miscellaneous: Add description which settings are used for the backups and link to the settings page

📋 Checklist

Please confirm the following (check all that apply):

• I have phpunit and/or behat tests that cover my changes or additions.
• Dont think this change needs any - can provide them if needed
• Code passes the code checker without errors and warnings.
• Code passes the moodle-ci/cd pipeline on all supported Moodle versions or the ones the plugin supports.
• One Random Timeout in last run
• Code does not have var_dump() or var_export or any other debugging statements (or commented out code) that
  should not appear on the productive branch.
• Code only uses language strings instead of hard-coded strings.

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🔍 Related Issues

• Related to Backup step should use backup::MODE_AUTOMATED instead of backup::MODE_GENERAL #304