chore: Update the gulp task for copying USWDS assets

[dzole0311]

Related Ticket: closes #1373

Description of Changes

The gulp task for copying the USWDS assets during deployment was not copying the assets at all. I've updated the task by replacing the generic uswds.copyImages() function with an explicit gulp task

Notes & Questions About Changes

• The change follows the same pattern as other copy tasks in our gulpfile
• No other configuration changes are needed as the task is already used into the existing build process

Validation / Testing

• In the deploy preview for veda-ui and veda-config-ghg (PR with deployment: Try out new gulp task for USWDS assets US-GHG-Center/veda-config-ghg#698), verify that USWDS icons appear correctly in the SiteAlert or Banner components
• Check if the icons appear when running the veda-ui locally

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[sandrahoang686]

ui and ghgh previews lgtm