refactor: updated swagger;

feat: helper function in errors for checking postgres error types;
feat: sql query method for finding users by their email;
feat: registration begin/complete with checking existing username/email;
refactor: error handling in controller

backend/docs/swagger.json

@@ -8,7 +8,7 @@
         "title": "Easywish client API",
         "contact": {},
         "license": {
-            "name": "GPL 3.0"
+            "name": "GPL-3.0"
         },
         "version": "1.0"
     },
@@ -135,7 +135,11 @@
                         }
                     }
                 ],
-                "responses": {}
+                "responses": {
+                    "200": {
+                        "description": "desc"
+                    }
+                }
             }
         },
         "/auth/registrationComplete": {
@@ -150,7 +154,25 @@
                     "Auth"
                 ],
                 "summary": "Confirm with code, finish creating the account",
-                "responses": {}
+                "parameters": [
+                    {
+                        "description": "desc",
+                        "name": "request",
+                        "in": "body",
+                        "required": true,
+                        "schema": {
+                            "$ref": "#/definitions/models.RegistrationCompleteRequest"
+                        }
+                    }
+                ],
+                "responses": {
+                    "200": {
+                        "description": "desc",
+                        "schema": {
+                            "$ref": "#/definitions/models.RegistrationCompleteResponse"
+                        }
+                    }
+                }
             }
         },
         "/profile": {
@@ -301,13 +323,16 @@
             ],
             "properties": {
                 "password": {
-                    "type": "string"
+                    "type": "string",
+                    "maxLength": 100
                 },
                 "totp": {
                     "type": "string"
                 },
                 "username": {
-                    "type": "string"
+                    "type": "string",
+                    "maxLength": 20,
+                    "minLength": 3
                 }
             }
         },
@@ -342,6 +367,46 @@
                     "minLength": 3
                 }
             }
+        },
+        "models.RegistrationCompleteRequest": {
+            "type": "object",
+            "required": [
+                "name",
+                "username",
+                "verification_code"
+            ],
+            "properties": {
+                "avatar_url": {
+                    "type": "string",
+                    "maxLength": 255
+                },
+                "birthday": {
+                    "type": "string"
+                },
+                "name": {
+                    "type": "string",
+                    "maxLength": 75
+                },
+                "username": {
+                    "type": "string",
+                    "maxLength": 20,
+                    "minLength": 3
+                },
+                "verification_code": {
+                    "type": "string"
+                }
+            }
+        },
+        "models.RegistrationCompleteResponse": {
+            "type": "object",
+            "properties": {
+                "access_token": {
+                    "type": "string"
+                },
+                "refresh_token": {
+                    "type": "string"
+                }
+            }
         }
     },
     "securityDefinitions": {