feat(api/v2): store user agent details in the session (#6711)

This change adds the ability to set and get user agent data, such as fingerprint, IP, request headers and a description to the session. All fields are optional.

Closes #6028

internal/domain/user_agent.go

@@ -0,0 +1,17 @@
+package domain
+
+import (
+	"net"
+	httplib "net/http"
+)
+
+type UserAgent struct {
+	FingerprintID *string        `json:"fingerprint_id,omitempty"`
+	IP            net.IP         `json:"ip,omitempty"`
+	Description   *string        `json:"description,omitempty"`
+	Header        httplib.Header `json:"header,omitempty"`
+}
+
+func (ua UserAgent) IsEmpty() bool {
+	return ua.FingerprintID == nil && len(ua.IP) == 0 && ua.Description == nil && ua.Header == nil
+}