Update variables and context

src/registrar/templates/emails/domain_invitation.txt

@@ -1,9 +1,7 @@
 {% autoescape off %}{# In a text file, we don't want to have HTML entities escaped #}
-Hi {{ incoming-email-here }}.
+Hi.
-# We don't know their first name until they make an account, we only know their email
-# Stuck here because we only get their email from the form, so can't pull above?
 
-{{ contact-of-whoever-owns-usually-admin-or-maybe-security-contact }} has added you as a manager on {{ domain.name }}.
+{{ first_name }} has added you as a manager on {{ domain.name }}.
 
 YOU NEED A LOGIN.GOV ACCOUNT
 You’ll need a Login.gov account to manage your .gov domain. Login.gov provides a simple and secure process for signing into many government services with one account. If you don’t already have one, follow these steps to create your Login.gov account <https://login.gov/help/get-started/create-your-account/>. 

src/registrar/views/domain.py

@@ -17,6 +17,7 @@ from django.views.generic.edit import FormMixin
 from registrar.models import (
     Domain,
     DomainInvitation,
+    DomainApplication,
     User,
     UserDomainRole,
 )
@@ -335,6 +336,7 @@ class DomainAddUserView(DomainPermissionView, FormMixin):
             )
         else:
             # created a new invitation in the database, so send an email
+            dapplication = DomainApplication.objects.filter(approved_domain__name=self.object.name)
             try:
                 send_templated_email(
                     "emails/domain_invitation.txt",
@@ -343,8 +345,7 @@ class DomainAddUserView(DomainPermissionView, FormMixin):
                     context={
                         "domain_url": self._domain_abs_url(),
                         "domain": self.object,
-                        # "user": the original person or contact
+                        "first_name": dapplication.first().creator,
-                        # "email": email of person we want to add
                     },
                 )
             except EmailSendingError: