Update Jira issues label colors

Because the colors in Jira hold meaning, we need to make sure that when
we display the Jira issue data in GitLab, that we translate/transfer the
colors over accurately.

Label colors in GitLab should be consistent with those that are found in
Jira, these are the hex color codes:
- Background: EBECF0
- Text color: 283856

ee/app/serializers/integrations/jira/issue_entity.rb

@@ -25,13 +25,10 @@ module Integrations
 
       expose :labels do |jira_issue|
         jira_issue.labels.map do |name|
-          bg_color = Label.color_for(name)
-          text_color = LabelsHelper.text_color_for_bg(bg_color)
-
           {
             name: name,
-            color: bg_color,
-            text_color: text_color
+            color: '#EBECF0',
+            text_color: '#283856'
 
           }
         end

ee/spec/serializers/integrations/jira/issue_entity_spec.rb

@@ -39,8 +39,8 @@ RSpec.describe Integrations::Jira::IssueEntity do
       labels: [
         {
           name: 'backend',
-          color: '#b43fdd',
-          text_color: '#FFFFFF'
+          color: '#EBECF0',
+          text_color: '#283856'
         }
       ],
       author: hash_including(name: 'reporter'),