feat: add first volunteer skill endpoint (add_skill) along with dtos

WebApp/Mapping/SkillMapping.cs

@@ -0,0 +1,25 @@
+using WebApp.DTOs;
+using WebApp.Entities;
+
+namespace WebApp.Mapping
+{
+    public static class SkillMapping
+    {
+        public static Skill ToSkillEntity(this SingleSkillDto SSDto, string name)
+        {
+            return new Skill()
+            {
+                SkillId = SSDto.Skill,
+                Name = name
+            };
+        }
+
+        public static SkillSummaryDto ToSkillSummaryDto(this Skill s)
+        {
+            return new SkillSummaryDto(
+                s.SkillId,
+                s.Name
+            );
+        }
+    }
+}