Polish Slack application edit page UI

What does this MR do and why?

Polish Slack application edit page UI:

• Use GLTable styles for the table.
• Adjust spacing and paddings.
• Update help text styles to match other integrations.

Screenshots or screen recordings

Scenario	Before	After
Slack application
Slack application (without integration)

How to set up and validate locally

1. Apply this patch.

diff --git a/ee/app/models/ee/integration.rb b/ee/app/models/ee/integration.rb
index 7b627abf3aa..521d0278e2b 100644
--- a/ee/app/models/ee/integration.rb
+++ b/ee/app/models/ee/integration.rb
@@ -22,7 +22,7 @@ module Integration
       override :project_specific_integration_names
       def project_specific_integration_names
         integrations = super + EE_PROJECT_SPECIFIC_INTEGRATION_NAMES
-        integrations += EE_COM_PROJECT_SPECIFIC_INTEGRATION_NAMES if ::Gitlab.com?
+        integrations += EE_COM_PROJECT_SPECIFIC_INTEGRATION_NAMES if ::Gitlab.dev_env_or_com?
         integrations
       end
     end
diff --git a/ee/app/models/ee/project.rb b/ee/app/models/ee/project.rb
index afb6f719622..ff7e9ce3de2 100644
--- a/ee/app/models/ee/project.rb
+++ b/ee/app/models/ee/project.rb
@@ -654,7 +654,11 @@ def disabled_integrations
         gh = github_integration_enabled? ? [] : %w[github]
         slack = ::Gitlab::CurrentSettings.slack_app_enabled ? %w[slack_slash_commands] : %w[gitlab_slack_application]
 
-        super + gh + slack
+        if Rails.env.development?
+          super
+        else
+          super + gh + slack
+        end
       end
     end
 

2. Go to rails console and run manually create a slack integration by running this:

p = Project.find 2 # You can use any project

i = p.create_gitlab_slack_application_integration

s = i.create_slack_integration

s.team_id = '12345'
s.team_name = 'any_string'
s.alias = 'gitlab-org/gitlab-shell'
s.user_id = 1 # This is usuall the `@root` user on GDK
s.save

3. Go to Project > Settings > Integrations > Slack application. The URL should look like this http://127.0.0.1:3000/gitlab-org/gitlab-shell/-/integrations/gitlab_slack_application/edit.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #345202 (closed)