Allow localhost or 127.0.0.1 to access api/health_checks without health-check-token (#8231)

* This change allows access to api/health_checks if you are coming from localhost
or 127.0.0.1. Pretty sweet huh?

The reason for this change is because I want to easily get to these healthcheck
end points from localhost without having to get the health-check-token beforehand.

Buttttt.... this addition has some issues. You can spoof the host header pretty
easily:

https://daniel.haxx.se/blog/2018/04/05/curl-another-host/

I thought about doing `return if !request.ssl? && request.local?`

to check of the request was over https or not. Any localhost healthcheck we do
directly to puma will be over http. Checking for TLS seemed like a logical next
check, but since we force https on the edge and not necessarily from the edge to
Puma the Host header can still be spoofed to get at these end points.

More info on host header attacks and what Rails 6 is doing about it:

https://github.com/rails/rails/issues/29893

While I do think it is a good idea to protect these healthcheck end points from
the outside world, I do want to be able to get to them easily locally. WWYD?

* Fix Health Check spec by stubbing request

Co-authored-by: mstruve <mollylbs@gmail.com>

app/controllers/api/v0/health_checks_controller.rb

@@ -34,6 +34,8 @@ module Api
       private
 
       def authenticate_with_token
+        return if request.local?
+
         key = request.headers["health-check-token"]
 
         return if key == SiteConfig.health_check_token

spec/requests/api/v0/health_checks_spec.rb

@@ -8,6 +8,7 @@ RSpec.describe "HealthCheck", type: :request do
 
   context "without a token" do
     it "returns an unauthorized request" do
+      allow_any_instance_of(ActionDispatch::Request).to receive(:remote_addr).and_return("0.0.0.0") # rubocop:disable RSpec/AnyInstance
       get app_api_health_checks_path
       expect(response.status).to eq(401)
     end