Add useful Cadence utility contracts

[sisyphusSmiling]

Description

Recommended by @btspoony, docs should include links to useful Cadence utilities. Some contracts to include off the bat:

• Contracts in https://github.com/green-goo-dao/flow-utils
• Base64Util - https://contractbrowser.com/A.a45ead1cf1ca9eda.Base64Util
• Serialize & SerializeMetadata found in https://github.com/onflow/flow-evm-bridge/tree/main

[btspoony]

BlockHole: https://github.com/fixes-world/token-list

• It can be used to vanish any FT without burn/destory (to keep totalSupply unchanged)

[btspoony]

Lost and found: https://github.com/Flowtyio/lost-and-found