Add higher dpi images for warning and info email icons

[shanechesnutt-ft]

🛠 Summary of changes

Replaced low resolution/dpi pngs with higher resolution/dpi pngs to improve look and feel of warning and info icons in emails.

👀 Screenshots

Before	After

[aduth]

One potential incompatibility here is with the tables reports mailers. It looks fine in the browser preview, but it relies on background-size to size the icon, which may not be broadly supported in common email clients:

https://www.caniemail.com/search/?s=background-size

Mailer example: http://localhost:3000/rails/mailers/report_mailer/fraud_metrics_report

A couple ideas, in order of preference:

• Update the tables report to use the inlined <img> like we're doing in other mailers
• Create a copy of the image at higher resolution to use when inlining element (e.g. info@4x.png), keeping info.png as-is
• Disregard whether it's broadly supported, since it's only used for non-production testing reports anyways (internal use only?)

[aduth]

I probably should have started with saying that this is a great change, happy to see it 👍 😄

As mentioned in Slack, we probably want to run these images through an optimizer like Squoosh to offset the potential file size increase.

[rutvigupta-design]

Approved from design, this looks so much better! 🎉 I'm curious about the considerations Andrew raised, so please let me know if design can support with anything else!

[gina-yamada]

I was digging around to see affects of change in background-image. I see that Andrew pointed out some concerns with this. Per his suggestion, it looks like you may need to rework the tables report a bit. Let me know if you need anything else reach out when this is ready for another review. TIL about http://localhost:3000/rails/mailers/report_mailer

[eileen-nava]

Thanks for catching this, the images definitely look better with higher dpi. I'm going to hold off approving, based on feedback from Andrew. Let me know if I can help with continued work on this task.