Add missing empty states in Admin Area

Description

Within the instance-level GitLab Admin Area, there are a lot of configuration options. Most of these are optional and naturally default to "not set up".
While few of these have a clear information structure and an engaging empty state (ConDev Index!), most of these pages lack UI polish today.

Proposal

Let's analyse and improve all pages and configurations that miss a user-friendly empty state within Admin Area, as a first step.
Please be aware that some of these empty states are not covering the full content page, but are part of additional page sections.

I'd love to encourage and see illustration ideas when we find time!

Table of content

• Admin Area/Overview/Runners
• Admin Area/Monitoring/Requests Profiles
• Admin Area/Monitoring/Health Check
• Admin Area/Monitoring/Audit Log
• Admin Area/System Hooks
• Admin Area/Applications
• Admin Area/Deploy Keys
• Admin Area/Labels

Cases

• Admin Area/Overview/Runners
  • Current: "No runners found" text
  • Planned: todo

Current	Proposal
	todo

• Admin Area/Monitoring/Requests Profiles
  • Current: "No profiles found" text
  • Planned: todo

Current	Proposal
	todo

• Admin Area/Monitoring/Health Check
  • Current: missing
  • Planned: todo

Current	Proposal
	todo

• Admin Area/Monitoring/Audit Log
  • Current: missing
  • Planned: todo
  • Low prio, will hardly ever be empty

Current	Proposal
todo	todo

• Admin Area/System Hooks: Plugins
  • Current: missing
  • Planned: todo

Current	Proposal
	todo

• Admin Area/Applications
  • Current: missing
  • Planned: todo

Current	Proposal
	todo

• Admin Area/Deploy Keys
  • Current: missing
  • Planned: todo

Current	Proposal
	todo

• Admin Area/Labels
  • Current: "There are no labels yet" text
  • Planned: Reuse existing project labels empty state

Current	Proposal

cc @hazelyang, @sarrahvesselov