Add Agent Skill

### Description

I know agents are good at discovering/learning CLIs, but it also might be good to have an official agent skill that can be used to make the experience more efficient.

### Acceptance Criteria

- [ ] Tell the agent you want to use agentcore cli to xyz and it loads the skill and understands the various configurations

### Additional Context

_No response_

No files, tests, or entry points are named. Start by locating the CLI's existing agent integration and configuration documentation, then determine how an official skill would be discovered and loaded. Done means an agent can request an agentcore CLI task, load the skill, and understand the relevant configurations.

Written by the indexing model from the issue text.