feat(skydiver-profile): add SkydiverProfile MySQL model and service

Introduces the skydiver_profile table as an optional 1-to-1 extension
of the user table, holding skydive-specific fields (licence, poids,
bg_image). Wired up with Sequelize associations and a service with
upsert support. Migration, model, relationships, and service layer
all included.

src/database/relationships/index.js

@@ -1,6 +1,9 @@
 const DB = require('../mysql');
 
 const associate = () => {
+    DB.User.hasOne(DB.SkydiverProfile, { as: 'skydiverProfile', foreignKey: 'userId', onDelete: 'CASCADE' });
+    DB.SkydiverProfile.belongsTo(DB.User, { as: 'user', foreignKey: 'userId' });
+
     DB.Article.belongsToMany(DB.Tag, { as: 'articleTags', through: DB.TagList, foreignKey: "articleId", otherKey: "tagName", onDelete: "CASCADE" });
     DB.Product.belongsToMany(DB.Tag, { as: 'productTags', through: DB.ProductTagXref, foreignKey: "productId", otherKey: "tagName", onDelete: "CASCADE" });
     DB.Article.belongsToMany(DB.User, { as: 'articleFavoriteUsers', through: DB.Favorite, foreignKey: "articleId", otherKey: "userId", onDelete: "CASCADE" });