Avro: Schema conversions should preserve docs

[shardulm94]

In Avro schema conversions referenced below, we should copy field level documentation between Iceberg and Avro schemas.

iceberg/core/src/main/java/org/apache/iceberg/avro/SchemaToType.java

Line 31 in 9f727cb

class SchemaToType extends AvroSchemaVisitor<Type> {

and

iceberg/core/src/main/java/org/apache/iceberg/avro/TypeToSchema.java

Line 34 in 9f727cb

class TypeToSchema extends TypeUtil.SchemaVisitor<Schema> {

[kbendick]

@shardulm94 @RussellSpitzer I can take this one.

[kbendick]

It seems my patch has inadvertently broken a different test (more info in the PR summary).

AFAIK I am unable to revert my PR to a draft as I don't have commit rights in this repo.

I've updated the PR to have [WIP] instead while I investigate.

[kbendick]

I figured out why the test needed to be updated (slight increase in manifest file size due to the field docs appearing in their header). Given the increase is many orders of magnitude less than the default target manifest file size (698 bytes increase per GenericManifestFile according to my debugger from this patch), I personally don't think it's an issue. I've left a comment on the PR in case anybody wants to weigh in on the slight size increase.

This PR is no longer considered WIP.

[shardulm94]

@kbendick Saw that your PR was merged. Thanks for working on this!