Rename gadget title option on Jira Server

Description

  • Jira Server only feature
  • Atlassian have added this feature on Cloud but they haven't added it on Server
  • There's even a JAC ticket with lots of votes: https://jira.atlassian.com/browse/JRASERVER-19766
  • This would be a useful feature for Custom Charts on Server and Data Center
  • The simplest way to add this for Custom Charts is to add an option next to the "Chart Title" input that changes the gadget heading instead of adding the title to the chart