feat: add configuration parsing and job definitions

Add a YAML config schema for migration jobs (source/target schema, table, primary key, options) and parse it at startup.

cmd/go_migrate/loader-error-handler.go

@@ -0,0 +1,65 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"sync"
+)
+
+type LoaderError struct {
+	Chunk
+	Msg string
+}
+
+func (e *LoaderError) Error() string {
+	return e.Msg
+}
+
+func loaderErrorHandler(
+	ctx context.Context,
+	chErrorsIn <-chan LoaderError,
+	chChunksOut chan<- Chunk,
+	chJobErrorsOut chan<- JobError,
+	wgActiveChunks *sync.WaitGroup,
+) {
+	for {
+		if ctx.Err() != nil {
+			return
+		}
+
+		select {
+		case <-ctx.Done():
+			return
+
+		case err, ok := <-chErrorsIn:
+			if !ok {
+				return
+			}
+
+			if err.RetryCounter >= maxRetryAttempts {
+				jobError := JobError{
+					ShouldCancelJob: false,
+					Msg:             fmt.Sprintf("chunk %v reached max retries (%d)", err.Id, maxRetryAttempts),
+					Prev:            &err,
+				}
+
+				select {
+				case chJobErrorsOut <- jobError:
+				case <-ctx.Done():
+					return
+				}
+
+				wgActiveChunks.Done()
+				continue
+			}
+
+			err.RetryCounter++
+
+			select {
+			case chChunksOut <- err.Chunk:
+			case <-ctx.Done():
+				return
+			}
+		}
+	}
+}