* refactor: migrator and introduce Store.(Create|Delete)Bucket
feat: kvmigration internal utility to create / managing kv store migrations
fix: ensure migrations applied in all test cases
* chore: update kv and migration documentation
This commit checks http.Request.Context().Err() to see if the context
has been canceled before writing an error code. It uses the non-standard
Nginx 499 error code for client disconnection.
Rohan Sreerama
George
Jonathan A. Sternberg
Alirie Gray
Johnny Steenbergen
Ben Johnson