add email validation

pro/controllers/users.go

@@ -206,6 +206,10 @@ func inviteUsers(w http.ResponseWriter, r *http.Request) {
 	}
 	for _, inviteeEmail := range inviteReq.UserEmails {
 		// check if user with email exists, then ignore
+		if !email.IsValid(inviteeEmail) {
+			logic.ReturnErrorResponse(w, r, logic.FormatError(errors.New("invalid email "+inviteeEmail), "badrequest"))
+			return
+		}
 		_, err := logic.GetUser(inviteeEmail)
 		if err == nil {
 			// user exists already, so ignore

pro/email/email.go

@@ -2,6 +2,7 @@ package email
 
 import (
 	"context"
+	"regexp"
 
 	"github.com/gravitl/netmaker/servercfg"
 )
@@ -52,3 +53,8 @@ type Notification struct {
 func GetClient() (e EmailSender) {
 	return client
 }
+
+func IsValid(email string) bool {
+	emailRegex := regexp.MustCompile(`^[a-z0-9._%+\-]+@[a-z0-9.\-]+\.[a-z]{2,4}$`)
+	return emailRegex.MatchString(email)
+}