www/mint-nft: Use Video NFT SDK instead of ethers!

[victorges]

What does this pull request do? Explain your changes. (required)

livepeer/video-nft#1

This is to POC the use of the Video NFT SDK with our own page for minting NFTs.

Still pending actually doing the file upload from the frontend page as well, to test
all the code in the SDK that was previously done by the CLI.

Specific updates (required)

• Replace ethers with @livepeer/video-nft
• ...

-

• How did you test each of these updates (required)
  Access /mint-nft and mint some stuff

https://livepeer-com-git-vg-featvideo-nft-sdk-use-livepeer.vercel.app/mint-nft

Does this pull request close any open issues?
Related to #929 but more stuff will be necessary (like docs).

Checklist:

• I have read the CONTRIBUTING document.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.

[vercel]

This pull request is being automatically deployed with Vercel (learn more).
To see the status of your deployment, click below or on the icon next to each commit.

🔍 Inspect: https://vercel.com/livepeer/livepeer-com/E4cGYap5QhsFePTiMH4Xy6veByCS
✅ Preview: https://livepeer-com-git-vg-featvideo-nft-sdk-use-livepeer.vercel.app

[figintern]

Cool stuff! Tried it out on the preview branch https://livepeer-com-git-vg-featvideo-nft-sdk-use-livepeer.vercel.app/mint-nft - the Polygon Testnet/Mainnet switching buttons are not working for me, but work for me on the current livepeer.com deployment (they open up a prompt in my metamask)

Not sure if this is because app is not running off the livepeer.com domain and there needs to be some whitelisting wired up - or the functionality is broken

Not seeing anything in the console logs when clicking these buttons on the preview branch URL either

[victorges]

Thanks @tqian1 ! Just fixed the switch network button.