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/models/mysql/index.js

@@ -10,6 +10,7 @@ exports.Product = require('./Product');
 exports.ProductCategoryXref = require('./ProductCategoryXref');
 exports.ProductTagXref = require('./ProductTagXref');
 exports.Role = require('./Role');
+exports.SkydiverProfile = require('./SkydiverProfile');
 exports.Tag = require('./Tag');
 exports.TagList = require('./TagList');
 exports.User = require('./User');