Add translation keys for sign-up page (#1505)

* Begin Work

* WIP

* WIP

* Finish adding notification keys

* WIP

* Finish work

* Fix lint error

* Re-organize Sign up page messages (#13)

- Re-order messages by their appearance in template
- Change the keys to conform to conventions
- Inline password mismatch notification message

---------

Co-authored-by: Sasha Sorokin <10401817+brawaru@users.noreply.github.com>
Co-authored-by: Prospector <6166773+Prospector@users.noreply.github.com>

locales/en-US/index.json

@@ -1,4 +1,43 @@
 {
+  "auth.sign-up.action.create-account": {
+    "message": "Create account"
+  },
+  "auth.sign-up.confirm-password.label": {
+    "message": "Confirm password"
+  },
+  "auth.sign-up.email.label": {
+    "message": "Email"
+  },
+  "auth.sign-up.label.username": {
+    "message": "Username"
+  },
+  "auth.sign-up.legal-dislaimer": {
+    "message": "By creating an account, you agree to Modrinth's <terms-link>Terms</terms-link> and <privacy-policy-link>Privacy Policy</privacy-policy-link>."
+  },
+  "auth.sign-up.notification.password-mismatch.text": {
+    "message": "Passwords do not match!"
+  },
+  "auth.sign-up.password.label": {
+    "message": "Password"
+  },
+  "auth.sign-up.sign-in-option.action": {
+    "message": "Sign in"
+  },
+  "auth.sign-up.sign-in-option.title": {
+    "message": "Already have an account?"
+  },
+  "auth.sign-up.subscribe.label": {
+    "message": "Subscribe to updates about Modrinth"
+  },
+  "auth.sign-up.title": {
+    "message": "Sign Up"
+  },
+  "auth.sign-up.title.create-account": {
+    "message": "Or create an account yourself"
+  },
+  "auth.sign-up.title.sign-up-with": {
+    "message": "Sign up with"
+  },
   "auth.verify-email.action.account-settings": {
     "message": "Account settings"
   },