ROUTE53: Adopt aws-sdk-go-v2 (#1321)

* Switch to aws-sdk-go-v2

AWS has released v2 of their SDK for Go.

See: https://aws.github.io/aws-sdk-go-v2/

One big advantage of this is no longer needing to export the
`AWS_SDK_LOAD_CONFIG=1` env var when using named profiles.

* Update integration test README

* Reenable pager601 and pager1201 integration tests for AWS Route53

* Implement intelligent batching for Route53 record changes

The AWS Route53 API for batch record changes limits the request size to
the smaller of:

- 1000 records.
- 32000 characters total for record values.

Also UPSERTs count as double (a DELETE and then a CREATE).

This commit changes how the record ChangeBatches are created to
respect these limits.

* Remove old comments

Co-authored-by: Tom Limoncelli <tlimoncelli@stackoverflow.com>

providers/route53/route53Provider_test.go

@@ -1,6 +1,13 @@
 package route53
 
-import "testing"
+import (
+	"fmt"
+	"reflect"
+	"testing"
+
+	"github.com/aws/aws-sdk-go-v2/aws"
+	r53Types "github.com/aws/aws-sdk-go-v2/service/route53/types"
+)
 
 func TestUnescape(t *testing.T) {
 	var tests = []struct {
@@ -22,3 +29,115 @@ func TestUnescape(t *testing.T) {
 		}
 	}
 }
+
+type batch struct {
+	start int
+	end   int
+}
+
+func (b batch) String() string {
+	return fmt.Sprintf("%d:%d", b.start, b.end)
+}
+
+func Test_changeBatcher(t *testing.T) {
+	genChanges := func(action r53Types.ChangeAction, typ r53Types.RRType, namePattern string, n int, targets ...string) []r53Types.Change {
+		changes := make([]r53Types.Change, n)
+		for i := 0; i < n; i++ {
+			changes[i].Action = action
+			changes[i].ResourceRecordSet = &r53Types.ResourceRecordSet{
+				Name: aws.String(fmt.Sprintf(namePattern, i)),
+				Type: typ,
+			}
+			for j := 0; j < len(targets); j++ {
+				changes[i].ResourceRecordSet.ResourceRecords = append(changes[i].ResourceRecordSet.ResourceRecords, r53Types.ResourceRecord{
+					Value: aws.String(targets[j]),
+				})
+			}
+		}
+		return changes
+	}
+
+	type fields struct {
+		changes  []r53Types.Change
+		maxSize  int
+		maxChars int
+	}
+	tests := []struct {
+		name    string
+		fields  fields
+		want    []batch
+		wantErr bool
+	}{
+		{
+			name: "one_batch",
+			fields: fields{
+				changes:  genChanges(r53Types.ChangeActionUpsert, r53Types.RRTypeA, "rec%04d", 99, "1.2.3.4"),
+				maxSize:  1000,
+				maxChars: 32000,
+			},
+			want: []batch{
+				{start: 0, end: 99},
+			},
+			wantErr: false,
+		},
+		{
+			name: "multi_batch_size",
+			fields: fields{
+				changes:  genChanges(r53Types.ChangeActionUpsert, r53Types.RRTypeA, "rec%04d", 2000, "1.2.3.4"),
+				maxSize:  1000,
+				maxChars: 32000,
+			},
+			want: []batch{
+				{start: 0, end: 500},
+				{start: 500, end: 1000},
+				{start: 1000, end: 1500},
+				{start: 1500, end: 2000},
+			},
+			wantErr: false,
+		},
+		{
+			name: "multi_batch_chars",
+			fields: fields{
+				changes:  genChanges(r53Types.ChangeActionCreate, r53Types.RRTypeTxt, "rec%04d", 1000, "1.2.3.4", "1.2.3.5", "1.2.3.6", "1.2.3.7", "1.2.3.8", "1.2.3.9"),
+				maxSize:  1000,
+				maxChars: 32000,
+			},
+			want: []batch{
+				{start: 0, end: 166},
+				{start: 166, end: 332},
+				{start: 332, end: 498},
+				{start: 498, end: 664},
+				{start: 664, end: 830},
+				{start: 830, end: 996},
+				{start: 996, end: 1000},
+			},
+			wantErr: false,
+		},
+	}
+	for i, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			b := &changeBatcher{
+				changes:  tt.fields.changes,
+				maxSize:  tt.fields.maxSize,
+				maxChars: tt.fields.maxChars,
+			}
+			got := make([]batch, 0)
+			for b.Next() {
+				start, end := b.Batch()
+				got = append(got, batch{
+					start: start,
+					end:   end,
+				})
+			}
+			err := b.Err()
+			if tt.wantErr && err == nil {
+				t.Errorf("%d: Expected an error, got nil", i)
+			} else if !tt.wantErr && err != nil {
+				t.Errorf("%d: Expected no error, got '%s'", i, err)
+			}
+			if !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("%d: Expected %s, got %s", i, tt.want, got)
+			}
+		})
+	}
+}