MM-28859 Add feature flag managment system using split.io and remove viper. (#15954)

* Add feature flag managment system using split.io and remove viper.

* Fixing tests.

* Attempt to fix postgres tests.

* Fix watch filepath for advanced logging.

* Review fixes.

* Some error wrapping.

* Remove unessisary store interface.

* Desanitize SplitKey

* Simplify.

* Review feedback.

* Rename split mlog adatper to split logger.

* fsInner

* Style.

* Restore oldcfg test.

* Downgrading non-actionable feature flag errors to warnings.

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

vendor/github.com/splitio/go-split-commons/v2/push/parser.go

@@ -0,0 +1,64 @@
+package push
+
+import (
+	"github.com/splitio/go-toolkit/v3/common"
+	"github.com/splitio/go-toolkit/v3/logging"
+)
+
+const (
+	update    = "update"
+	errorType = "error"
+	occupancy = "[meta]occupancy"
+)
+
+// NotificationParser struct
+type NotificationParser struct {
+	logger logging.LoggerInterface
+}
+
+// NewNotificationParser creates notifcation parser
+func NewNotificationParser(logger logging.LoggerInterface) *NotificationParser {
+	return &NotificationParser{
+		logger: logger,
+	}
+}
+
+// Parse parses incoming event from streaming
+func (n *NotificationParser) Parse(event map[string]interface{}) IncomingEvent {
+	incomingEvent := IncomingEvent{
+		id:       common.AsStringOrNil(event["id"]),
+		encoding: common.AsStringOrNil(event["encoding"]),
+		data:     common.AsStringOrNil(event["data"]),
+		name:     common.AsStringOrNil(event["name"]),
+		clientID: common.AsStringOrNil(event["clientId"]),
+		channel:  common.AsStringOrNil(event["channel"]),
+		message:  common.AsStringOrNil(event["message"]),
+		href:     common.AsStringOrNil(event["href"]),
+	}
+
+	timestamp := common.AsFloat64OrNil(event["timestamp"])
+	if timestamp != nil {
+		incomingEvent.timestamp = common.Int64Ref(int64(*timestamp))
+	}
+	code := common.AsFloat64OrNil(event["code"])
+	if code != nil {
+		incomingEvent.code = common.IntRef(int(*code))
+	}
+	statusCode := common.AsFloat64OrNil(event["statusCode"])
+	if statusCode != nil {
+		incomingEvent.statusCode = common.IntRef(int(*statusCode))
+	}
+
+	if incomingEvent.code != nil && incomingEvent.statusCode != nil {
+		incomingEvent.event = errorType
+		return incomingEvent
+	}
+
+	if incomingEvent.name != nil && *incomingEvent.name == occupancy {
+		incomingEvent.event = occupancy
+		return incomingEvent
+	}
+
+	incomingEvent.event = update
+	return incomingEvent
+}