Column Topic Schema Evolution

[sehz]

Per #3081. Producer/SPU need to encode/decode column values from/into a record. This will turn Fluvio topic into something like Write Ahead Log.

Given schema can be changed anytime, record data need to track following schema evolution. The schema will follow SemVer policy.

Minor version changes:

• Column addition

Other changes are consider major version changes:

• Column deletion
• Column Renaming
• Column type changes

Any major schema changes will save previous version automatically. Latest schema will be always active schema. Deletion of previous version is only allowed if no data references old schema.

Column records then will use following format

column_id:     u16
total_len:   u16
column_count: u8
column0
column1
column2
column3

[github-actions]

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