[FEATURE] Add issue template for user reactivation process

.gitlab/issue_templates/UserReactivationProcess.md

+**Who wants to be recovered:**
+
+> Insert request  
+
+**old username** 
+
+
+**old e-mail adress**
+
+
+**Process steps**
+
+* [ ]  user needs to confirm his old e-mail adress (reply with old adress)
+* [ ]  recover the user via backend