utils: new error package

[xhebox]

A simpler error package to replace pingcap/errors

Signed-off-by: xhe [email protected]

What problem does this PR solve?

Ref #8. A rewritten of the old package. If we don't process SQL statements, then neither terror nor pingcap/errors is necessary. This small wrapper package is enough.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Code changes

• Has configuration change
• Has HTTP API interfaces change (Don't forget to add the declarative for API)
• Has persistent data change

Release note

• No release note