Add missing error codes to REST spec

[jackye1995]

Apache Iceberg version

None

Query engine

None

Please describe the bug 🐞

There are a few important error codes missing in the REST spec, including:

• 408 Request Timeout
• 413 Payload Too Large
• 414 URI Too Long
• 426 Upgrade Required
• 429 Too Many Requests
• 431 Request Header Fields Too Large
• 500 Internal Server Error
• 504 Gateway Timeout

We need to do a full pass and properly define the expected behaviors that maps to these error codes.