Support delete and update operations in MySQL writer.

[ibuenros]

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

• [ ] 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-XXX

Description

• [ ] Here are some details about my PR, including screenshots (if applicable): Makes various improvements to MySQL writer:
• Switches from using Gobblin JdbcTypes to native java JDBCTypes
• Use JDBC metadata to retrieve column information/primary keys
• Support for delete and updates for JDBC writer, implementation for MySQL.
• Refactoring of avro to JDBC converter to support extension.

Tests

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

Commits

• [ ] 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"

[ibuenros]

@htran1 can you review?