style: update 'external URL' copies and add buttons animations

[RominaMarchetti]

What does this PR change?

This PR updates the copies of the modal and add the missing animations on the buttons. Additionally, the checkmark container asset changed for a white squared instead of a transparent one.
Observe that the 'domain' text field has been remove leaving the link visible only.

BEFORE

AFTER

How to test the changes?

1. Launch the explorer.
2. To open the modal, click the 'Discord' or 'X' buttons located at the spawn point platform in Genesis Plaza. Validate the hover/press animation is working in both main buttons.
3. Check the checkbox container has been updated with the correct white style.

[github-actions]

Windows and Mac build successfull in Unity Cloud! You can find a link to the downloadable artifact below.

Name	Link
Commit	3272510
Logs	https://github.com/decentraland/unity-explorer/actions/runs/13052358454
Download Windows	https://github.com/decentraland/unity-explorer/suites/33719462632/artifacts/2510557782
Download Windows S3	https://explorer-artifacts.decentraland.org/@dcl/unity-explorer/branch/style/url-modal-update-copy-and-animations/Decentraland_windows64.zip
Download Mac	https://github.com/decentraland/unity-explorer/suites/33719462632/artifacts/2510614963
Download Mac S3	https://explorer-artifacts.decentraland.org/@dcl/unity-explorer/branch/style/url-modal-update-copy-and-animations/Decentraland_macos.zip
Built on	2025-01-30T13:13:19Z

[DafGreco]

Fix implemented on both platforms ! ✅

PR check on windows :

• Discord modal New UI ✅
• X modal New UI ✅

✅ the checkbox is working.
✅ Continue button is currently working
✅ Cancel button is currently working

Sanity check made on this PR :

• Teleport (Dollhouse/ the inn / Metadynelabs)
• Profile customization
• Camera functionality
• Gallery
• Map functionality
• Backpack
• Skybox
• Emotes

PR check on macos :

• Discord modal New UI ✅
• X modal New UI ✅

✅ the checkbox is working.
✅Continue button is currently working
✅ Cancel button is currently working

Sanity check done on this PR:

• Profile customization
• Backpack
• Teleport : dollhouse / the inn / metadynelabs
• Badges
• Notifications
• Skybox
• map functionality
• Emotes
• camera functionality / Gallery

Before this fix :

After the fix has been implemented :

[DafGreco]

Fix implemented on both platforms ! ✅

PR check on windows :

• Discord modal New UI ✅
• X modal New UI ✅

✅ the checkbox is working.
✅ Continue button is currently working
✅ Cancel button is currently working

Sanity check made on this PR :

• Teleport (Dollhouse/ the inn / Metadynelabs)
• Profile customization
• Camera functionality
• Gallery
• Map functionality
• Backpack
• Skybox
• Emotes

PR check on macos :

• Discord modal New UI ✅
• X modal New UI ✅

✅ the checkbox is working.
✅Continue button is currently working
✅ Cancel button is currently working

Sanity check done on this PR:

• Profile customization
• Backpack
• Teleport : dollhouse / the inn / metadynelabs
• Badges
• Notifications
• Skybox
• map functionality
• Emotes
• camera functionality / Gallery

Before this fix :

After the fix has been implemented :