v3(services): read service documentationUrl correctly

Brokers return 'documentationUrl' rather than 'documentation_url'
in metadata

[#173447953](https://www.pivotaltracker.com/story/show/173447953)

Author: Brian Butz

app/decorators/field_service_instance_offering_decorator.rb

@@ -46,7 +46,7 @@ def decorate(hash, service_instances)
 
     def extract_documentation_url(extra)
       metadata = JSON.parse(extra)
-      metadata['documentation_url']
+      metadata['documentationUrl']
     rescue JSON::ParserError
       nil
     end

app/presenters/v3/service_offering_presenter.rb

@@ -58,7 +58,7 @@ def shareable(metadata)
         end
 
         def documentation_url(metadata)
-          metadata['documentation_url'] || ''
+          metadata['documentationUrl'] || ''
         end
 
         def broker_metadata

spec/support/fakes/blueprints.rb

@@ -305,7 +305,7 @@ module VCAP::CloudController
     active                { true }
     service_broker        { ServiceBroker.make }
     description           { Sham.description } # remove hack
-    extra                 { '{"shareable": true, "documentation_url": "https://some.url.for.docs/"}' }
+    extra                 { '{"shareable": true, "documentationUrl": "https://some.url.for.docs/"}' }
     instances_retrievable { false }
     bindings_retrievable  { false }
     plan_updateable       { false }

spec/unit/decorators/field_service_instance_offering_decorator_spec.rb

@@ -4,8 +4,8 @@
 module VCAP::CloudController
   RSpec.describe FieldServiceInstanceOfferingDecorator do
     describe '.decorate' do
-      let(:offering1) { Service.make(extra: '{"documentation_url": "https://offering1.com"}') }
-      let(:offering2) { Service.make(extra: '{"documentation_url": "https://offering2.com"}') }
+      let(:offering1) { Service.make(extra: '{"documentationUrl": "https://offering1.com"}') }
+      let(:offering2) { Service.make(extra: '{"documentationUrl": "https://offering2.com"}') }
 
       let(:plan1) { ServicePlan.make(service: offering1) }
       let(:plan2) { ServicePlan.make(service: offering2) }

spec/unit/presenters/v3/service_offering_presenter_spec.rb

@@ -191,7 +191,7 @@
       end
 
       context 'when `documentation_url` is set' do
-        let(:extra) { '{"documentation_url": "https://some.documentation.url/"}' }
+        let(:extra) { '{"documentationUrl": "https://some.documentation.url/"}' }
 
         it 'displays the value` as a top level field' do
           expect(result[:documentation_url]).to eq 'https://some.documentation.url/'