Freshsales integration (#1782)

* Add FreshsalesController

* Add better errors

* Fix formatting issues

* Add comments

* Add Billing.Test to solution files

* Fix unit test

* Format code

* Address PR feedback

test/Common/AutoFixture/Attributes/RequiredEnvironmentTheoryAttribute.cs

@@ -0,0 +1,39 @@
+using System;
+using Xunit;
+
+namespace Bit.Test.Common.AutoFixture.Attributes
+{
+    /// <summary>
+    /// Used for requiring certain environment variables exist at the time. Mostly used for more edge unit tests that shouldn't
+    /// be run during CI builds or should only be ran in CI builds when pieces of information are available.
+    /// </summary>
+    public class RequiredEnvironmentTheoryAttribute : TheoryAttribute
+    {
+        private readonly string[] _environmentVariableNames;
+
+        public RequiredEnvironmentTheoryAttribute(params string[] environmentVariableNames)
+        {
+            _environmentVariableNames = environmentVariableNames;
+
+            if (!HasRequiredEnvironmentVariables())
+            {
+                Skip = $"Missing one or more required environment variables. ({string.Join(", ", _environmentVariableNames)})";
+            }
+        }
+
+        private bool HasRequiredEnvironmentVariables()
+        {
+            foreach (var env in _environmentVariableNames)
+            {
+                var value = Environment.GetEnvironmentVariable(env);
+
+                if (value == null)
+                {
+                    return false;
+                }
+            }
+
+            return true;
+        }
+    }
+}