Add images data source to wallet page and panel

[spylogsster]

Resolves brave/brave-browser#20650

Icons can be added this way:

<img src="chrome://image?https://brave.com/static-assets/images/brave-favicon.png"></img>

// The sanitized image source provides a convenient mean to embed images into
// WebUIs. For security reasons WebUIs are not allowed to download and decode
// external images in their renderer process. The sanitized image source allows
// external images in WebUIs by downloading the image in the browser process,
// decoding the image in an isolated utility process, re-encoding the image as
// PNG and sending the now sanitized image back to the requesting WebUI. You can
// reach the image source via:
//
//   chrome://image?<external image URL>

More details:
https://source.chromium.org/chromium/chromium/src/+/main:chrome/browser/ui/webui/sanitized_image_source.h;l=37?q=SanitizedImageSource&ss=chromium

Used in Chrome NTP page https://source.chromium.org/chromium/chromium/src/+/main:chrome/browser/ui/webui/new_tab_page/new_tab_page_ui.cc;l=390?q=SanitizedImageSource%20&ss=chromium

Submitter Checklist:

• I confirm that no security/privacy review is needed, or that I have requested one
• There is a ticket for my issue
• Used Github auto-closing keywords in the PR description above
• Wrote a good PR/commit description
• Squashed any review feedback or "fixup" commits before merge, so that history is a record of what happened in the repo, not your PR
• Added appropriate labels (QA/Yes or QA/No; release-notes/include or release-notes/exclude; OS/...) to the associated issue
• Checked the PR locally: npm run test -- brave_browser_tests, npm run test -- brave_unit_tests, npm run lint, npm run gn_check, npm run tslint
• Ran git rebase master (if needed)

Reviewer Checklist:

• A security review is not needed, or a link to one is included in the PR description
• New files have MPL-2.0 license header
• Adequate test coverage exists to prevent regressions
• Major classes, functions and non-trivial code blocks are well-commented
• Changes in component dependencies are properly reflected in gn
• Code follows the style guide
• Test plan is specified in PR before merging

After-merge Checklist:

• The associated issue milestone is set to the smallest version that the
  changes has landed on
• All relevant documentation has been updated, for instance:
  • https://github.com/brave/brave-browser/wiki/Deviations-from-Chromium-(features-we-disable-or-remove)
  • https://github.com/brave/brave-browser/wiki/Proxy-redirected-URLs
  • https://github.com/brave/brave-browser/wiki/Fingerprinting-Protections
  • https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes
  • https://github.com/brave/brave-browser/wiki/Custom-Headers
  • https://github.com/brave/brave-browser/wiki/Web-Compatibility-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Test Plan:

• No manual tests required

[bbondy]

Approved but let's ask @fmarier / @diracdeltas to be sure.