Support for renaming fields

[Fryuni]

Avro schema evolution supports field renaming by setting the old name as an alias of the new name on the new schema.

If a field is missing on BigQuery is missing from the schema but is an alias to some other field, currently, this causes an impossible update, but there is no need to update the table schema since this is a backward-compatible schema evolution for Avro.

[saumyasuhagiya]

have you checked https://docs.confluent.io/platform/current/connect/transforms/replacefield.html ? @Fryuni

[Fryuni]

The problem is not the data, we do use a transformer to make the data itself compatible with the previous version (a custom one).

The connector reads directly from the registry the latest version and tries to update the schema with the new column, this happens before attempting to write the data.

[Fryuni]

I reopened this issue on the new repo at confluentinc#203