Parse binlog timestamp in UTC

[meiji163]

Description

This PR addresses a situation where TIMESTAMP fields can be corrupted. Quoting @dm-2:

gh-ost is incorrectly modifying the timezone of timestamp fields of rows when the following criteria are met:

• database is running in non-UTC timezone, and
• row is changed whilst a migration is running, and
• field is timestamp, and
• field contains a non-UTC timestamp

This is caused by how go-mysql/replication package parses binlog timestamps based on timezone. In the latest release this behaviour was disabled by editing the vendored package 7e0bdbe , but in the master branch it is enabled.

• contributed code is using same conventions as original code
• script/cibuild returns with no formatting errors, build errors or unit test errors.

[meiji163]

This has run successfully on testing replicas on 175 production tables total, so I am fairly confident to merge.

[timvaillancourt]

@meiji163 I'm so glad someone finally figured this out and it's great it didn't require modifying vendored code. Thank you!