Standardize Agent naming

Problem to solve

On the Kubernetes clusters page -/clusters there is an inconsistent naming convention for GitLab Agent

• Card text - GitLab Agent
• Install new agent button - agent (lowercase)
• Action options - Agent (uppercase)
• Table heading - X agents
• Docs - GitLab Agent for Kubernetes
• Docs mentions - (“Agent”, for short)

Proposal

Use a consistent naming convention to refer to the Gitlab Agent by making the following updates:

• No agents available
• Actions > Connect with an agent
• Install a new agent
• Securely connect your Kubernetes clusters to GitLab by using an agent<link>. You can deploy your applications, run your pipelines, use Review Apps, and much more.