Impl rest catalog + table updates & requirements

[jwtryg]

Hi @zeroshade

I think it's really cool that you are working on a golang-iceberg implementation, and I would like to contribute if I can. I have tried to finish the rest catalog implementation, and then I have added table updates and requirements, using a new MetadataBuilder struct that can simplify updating metadata. Like the existing implementation, I have tried to stay close to the pyIceberg implementation.

I thought this could be a good starting point for also implementing transactions and table updates. I would love to get your input and change/adjust the implementation accordingly.