feat: implement caldav search

vendor/github.com/dolanor/caldav-go/webdav/entities/propfind.go

@@ -0,0 +1,20 @@
+package entities
+
+import "encoding/xml"
+
+// a request to find properties on an an entity or collection
+type Propfind struct {
+	XMLName xml.Name `xml:"DAV: propfind"`
+	AllProp *AllProp `xml:",omitempty"`
+	Props   []*Prop  `xml:"prop,omitempty"`
+}
+
+// a propfind property representing all properties
+type AllProp struct {
+	XMLName xml.Name `xml:"allprop"`
+}
+
+// a convenience method for searching all properties
+func NewAllPropsFind() *Propfind {
+	return &Propfind{AllProp: new(AllProp)}
+}