chore: redeploy TierNFT contract and change testnet references. Mumbai is deprecating

[elPiablo]

Mumbai is being retired. TierNFT lesson and Connect to Front-end lessons need upgraded:

https://polygon.technology/blog/polygon-pos-is-cooking-the-napoli-upgrade-means-better-ux-the-mumbai-testnet-takes-a-bow

• [x] remove reference to "scripts/ where simple automation scripts go"

• [x] change to rm contracts/*.sol rm test/*.js by removing rm scripts/*.js as it doesn't come with the build anymore

• [x] change hardhat.config.js with new RPC details: https://polygon.technology/blog/polygon-pos-and-polygon-zkevm-new-testnets-for-polygon-protocols for Amoy Testnet

• [x] update "Adding the testnet network paragraph with new details 👆🏼

• [x] update screenshot from Mumbai to Amoy

• [x] check if URL for test token faucet is correct - add alternatives or additional URL possibilites

• [x] update screenshot re: faucet if necessary

• [x] under Personal Security paragraph, format the current paragraph from text to a bulleted list for Zerion steps

• [x] change deploy command to npx hardhat run scripts/deploy.js --network amoy

• [x] change mint command to npx hardhat run scripts/mint.js --network amoy