Implement audit logging functionality across services and middleware

- Introduced a new `auditlog` package to handle audit logging for user actions, including creation, updates, deletions, and authentication events.
- Enhanced existing services (customer, user) to log relevant actions using the new audit logger, capturing details such as actor ID, action type, target type, and success status.
- Added middleware to enrich request context with metadata for audit logging, ensuring comprehensive tracking of user interactions.
- Integrated Elasticsearch for persistent storage of audit logs, with fallback to file-only logging if Elasticsearch is unavailable.
- Updated API documentation to include new audit log endpoints for administrative access.

This update significantly improves the system's ability to track and audit user actions, enhancing security and accountability within the application.

internal/auditlog/entity.go

@@ -0,0 +1,31 @@
+package auditlog
+
+// Entry represents an audit log record returned by the API.
+type Entry struct {
+	ActorID    string            `json:"actor_id"`
+	ActorType  string            `json:"actor_type"`
+	Action     string            `json:"action"`
+	TargetType string            `json:"target_type"`
+	TargetID   string            `json:"target_id"`
+	At         int64             `json:"at"`
+	IP         string            `json:"ip,omitempty"`
+	RequestID  string            `json:"request_id,omitempty"`
+	UserAgent  string            `json:"user_agent,omitempty"`
+	Success    bool              `json:"success"`
+	Metadata   map[string]string `json:"metadata,omitempty"`
+}
+
+// ListResponse is the paginated audit log list response.
+type ListResponse struct {
+	Logs []*Entry       `json:"logs"`
+	Meta *ListMeta      `json:"meta,omitempty"`
+}
+
+// ListMeta contains pagination metadata.
+type ListMeta struct {
+	Total  int64 `json:"total"`
+	Limit  int   `json:"limit"`
+	Offset int   `json:"offset"`
+	Page   int   `json:"page"`
+	Pages  int   `json:"pages"`
+}