feat(signup-api): implement user signup endpoint

 - setup test suite for user signup endpoint
 - install `bcrypt` to encrypt user password
 - install `cross-env` to set environment variables
 - install `babel-eslint` to lint all babel code
 - install `nodemon` to monitor changes in code
 - Install `core-js` and `@babel/runtime-corejs3` to emulate a full ES2015+ environment
 - create a helper class to encrypt password
 - create a utility class to handle responses
 - create a service class to mediate between database and user controller
 - create a controller class to implement signup endpoint
 - add the route
 - test with postman
 - ensure all test cases are passing
 - document with Swagger

[Delivers #168188701]

.babelrc

@@ -1,3 +1,8 @@
 {
-    "presets": ["@babel/preset-env"]
+    "presets": ["@babel/preset-env"],
+    "plugins": [
+        ["@babel/transform-runtime", {
+          "corejs": 3,
+        }]
+      ]
 }

.env.example

@@ -1,3 +1,3 @@
-PORT=5000
+PORT=3000
 DATABASE_DEV_URL= postgres://user:password@127.0.0.1:5432/database_name
 DATABASE_TEST_URL= postgres://user:password@127.0.0.1:5432/database_name

.eslintrc.json

@@ -6,6 +6,7 @@
     "es6": true,
     "mocha": true
     },
+    "parser": "babel-eslint",
     "parserOptions": {
     "no-undefined": 0,  
     "ecmaVersion": 6,
@@ -22,6 +23,7 @@
     "no-param-reassign": 0,
     "comma-dangle": 0,
     "curly": ["error", "multi-line"],
+    "arrow-parens": ["error", "as-needed"],
     "import/no-unresolved": [2, { "commonjs": true }],
     "import/no-extraneous-dependencies": ["error", {"devDependencies": true}],
     "no-shadow": ["error", { "allow": ["req", "res", "err"] }],