Register new Agent UI
## Release notes
The GitLab Kubernetes Agent allows a secure bi-directional connection between GitLab and any Kubernetes cluster. Previously, setting up the Kubernetes Agent required GraphQL API calls, a step that discouraged users from adopting the Agent. GitLab now ships with a dedicated user interface to set up new Kubernetes Agents.
## Scope
- on the agent list page have a dialog that asks
- the agent name
- the token name (default = "Agent access token - 1")
- token description (optional, default = "")
- show the token with the 1-liner installer in place of the form, in the dialog
- when we close the dialog reload the list of agents / show the new agent too
## Proposal
See design issue: https://gitlab.com/gitlab-org/gitlab/-/issues/321408/
epic