Adds AfterError callback hook

[guilhermefbarbosa]

• Do only one thing
• Non breaking API changes
• Tested

What did this pull request do?

This pull request adds an new callback hook: AfterError that should run if any other main callback returns an error.

Currently, AfterXYZ hooks like AfterCreate, AfterSave and AfterUpdate doesn't get executed when an error is found, this leads to some unnecessary (but not always a problem) levels of code coupling between applications and errors returned by gorm.

User Case Description

There are many possible use cases, but mainly:

1. Use AfterError hooks to translate/wrap gorm and database errors to application domain errors, decoupling other application layers from duty of knowing external errors.
2. Use AfterError to handle specific table-wise errors, like UniqueIndex errors to redirect application flow

[guilhermefbarbosa]

i'm looking over these test failures

[a631807682]

What is the difference between this feat and https://gorm.io/docs/write_plugins.html#Register-Callback-with-orders

[jinzhu]

Doesn't seem necessary for me.