Advertisement helper improvements

[Oaphi]

• Prevent malicious icon_path from executing system commands - See Security/Open cop for details;
• Only allow safe URIs (HTTP, HTTP(S), or relative) for icon_path;

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.35%. Comparing base (612ac9b) to head (af933d1).
⚠️ Report is 4 commits behind head on develop.

Additional details and impacted files

Components	Coverage Δ
controllers	77.02% <ø> (ø)
helpers	85.47% <100.00%> (ø)
jobs	79.93% <ø> (ø)
models	93.48% <ø> (ø)
tasks	61.11% <ø> (ø)
scripts	∅ <ø> (∅)

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[Oaphi]

Blocked by: #2154 (I'd like to use the URI helper)