PoC: Introduce column update metadata

[gaborkaszab]

Content:

• Column update table metadata
• API to write column update metadata
• Changes to read and write column update metadata to manifest entries
• Bunch of TODOs :)

Details:

• No overlap in field IDs across column updates. Overlapping field IDs removed from older column updates when committing a new one
• Column updates covers entire data files (no partial column updates)
• Follow the approach from the proposal where manifests are cloned with same content but new column update metadata
• Other approach (delete manifest + new manifest file) depends on V4, not covered now
• Integrated into V3 metadata with made up field IDs. Will have to adjust for V4 once available