fix: Add IOTX icon (#26723)

## **Description**

Adds icons for IoTeX network: https://chainlist.org/chain/4689

[![Open in GitHub
Codespaces](https://github.com/codespaces/badge.svg)](https://codespaces.new/MetaMask/metamask-extension/pull/26723?quickstart=1)

## **Related issues**

Fixes: https://consensyssoftware.atlassian.net/browse/MMASSETS-353

## **Manual testing steps**

1. Add IoTeX network as custom network
2. Icon should display in Network List as well as Native token for IoTeX

## **Screenshots/Recordings**

<img width="362" alt="Screenshot 2024-08-28 at 8 38 03 AM"
src="https://github.com/user-attachments/assets/fe6f3ef5-aa8c-4309-8bc7-39d711297ff7">

## **Pre-merge author checklist**

- [x] I've followed [MetaMask Contributor
Docs](https://github.com/MetaMask/contributor-docs) and [MetaMask
Extension Coding
Standards](https://github.com/MetaMask/metamask-extension/blob/develop/.github/guidelines/CODING_GUIDELINES.md).
- [x] I've completed the PR template to the best of my ability
- [x] I’ve included tests if applicable
- [x] I’ve documented my code using [JSDoc](https://jsdoc.app/) format
if applicable
- [x] I’ve applied the right labels on the PR (see [labeling
guidelines](https://github.com/MetaMask/metamask-extension/blob/develop/.github/guidelines/LABELING_GUIDELINES.md)).
Not required for external contributors.

## **Pre-merge reviewer checklist**

- [ ] I've manually tested the PR (e.g. pull and build branch, run the
app, test code being changed).
- [ ] I confirm that this PR addresses all acceptance criteria described
in the ticket it closes and includes the necessary testing evidence such
as recordings and or screenshots.