Allow specifying target in ui-control

[cgjgh]

Description

Allows specifying a target along with url in order to open external links in new tabs

msg.payload = {
    url: 'https://nodered.org',
    target: '_blank'
}

Related Issue(s)

Closes #1163

Checklist

• I have read the contribution guidelines
• Suitable unit/system level tests have been added and they pass
• Documentation has been updated
  • Upgrade instructions
  • Configuration details
  • Concepts
• Changes flowforge.yml?
  • Issue/PR raised on FlowFuse/helm to update ConfigMap Template
  • Issue/PR raised on FlowFuse/CloudProject to update values for Staging/Production

Labels

• Includes a DB migration? -> add the area:migration label