[GOBBLIN-443] Avro to CSV Converter

[abti]

Dear Gobblin maintainers,

Please accept this PR. I understand that it will not be reviewed until I have checked off all the steps below!

JIRA

• [x] My PR addresses the following Gobblin JIRA issues and references them in the PR title. For example, "[GOBBLIN-XXX] My Gobblin PR"
  • https://issues.apache.org/jira/browse/GOBBLIN-443

Description

• [x] Here are some details about my PR, including screenshots (if applicable): A converter for Avro to CSV. It assumes that Schema is of type Record, and the does not has nested fields. In case of nested fields, they will be serialized to string by implicit toString provided by Avro library.

Tests

• [x] My PR adds the following unit tests OR does not need testing for this extremely good reason: AvroToCsvConverterTest

Commits

• [x] My commits all reference JIRA issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"