Add the emailer route to the adopt a tree route

[fzyang1227]

Why

• to provide a email with specific next steps in terms of taking care of the tree/etc.
• to send the email to the user upon adoption (automatic email)

What to do

• create a basic (dummy) template for a sample email via the template route (this will be provided later to be fully implemented
• add the emailer route to the adopt a tree route
  • grab the user's email in order to send it to them
  • grab the template and send it to the email
  • reference of the welcome email on lines 45-56
• note: see what is possible to protect this call (i.e. not let a user spam adopt/unadopt to send a ton of emails/requests)