Add new rule EC31: Prefer lighter formats for image files

[salah-dev-inp]

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[dedece35]

I mark this PR as Draft until decision about all PRs about the same subject :

• [EC203] Detect unoptimized image format creedengo-java#47
• add new rules for EC203 creedengo-java#55
• [EC203][Java] Detect unoptimized image format #324
• Add new rule EC31: Prefer lighter formats for image files #330
• Add new rule EC31: Prefer lighter formats for image files creedengo-java#52
• Add rule "Prefer lighter formats for image files" creedengo-javascript#46
• Add rule "Prefer lighter formats for image files" #269
• Add rule "Prefer lighter formats for image files" #335

check comment about the subject in PR green-code-initiative/creedengo-java#47

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This PR has been automatically marked as stale because it has no activity for 60 days.
Please add a comment if you want to keep the issue open. Thank you for your contributions!