Refactor curl command doc

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What does this MR do and why?

References

Fixes #509818

• Refactored the curl command for doc/api/issue_links.md

Screenshots or screen recordings

Before	After

How to set up and validate locally

To test locally run: http:127.0.0.1:3000/help/api/issue_links

If running into redirection issues, take a look at the following steps:

1. Inspect the runtime config and application settings that control help pages

   bundle exec rails runner "
   puts 'Settings.gitlab_docs.enabled=' + (Settings.gitlab_docs.enabled rescue 'nil').to_s
   puts 'Settings.gitlab_docs.host=' + (Settings.gitlab_docs.host rescue 'nil').to_s
   puts 'ApplicationSetting.help_page_documentation_base_url=' + (Gitlab::CurrentSettings.current_application_settings.help_page_documentation_base_url rescue 'nil').to_s
   "

   2. Cleared the ApplicationSetting value (temporary fix in the running instance)

   bundle exec rails runner "
   puts 'Before=' + (Gitlab::CurrentSettings.current_application_settings.help_page_documentation_base_url.inspect)
   Gitlab::CurrentSettings.current_application_settings.update!(help_page_documentation_base_url: '')
   puts 'After=' + (Gitlab::CurrentSettings.current_application_settings.help_page_documentation_base_url.inspect)
   "

   3. Verified the help page now renders locally

   curl -i http://127.0.0.1:3000/help/api/issue_links

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