Add update primitive (similar to agentcore configure)

### Description

While editing `agentcore.json` is one option, customers leverage the CLI are accustomed to primitives for create, delete **and** update.

Take adding memory to an existing agent, for an example. Today, you'd have to do something like this:

```
agentcore remove agent --name personalAgent
agentcore add agent \
--type byo \
--name personalAgent \
--code-location ./app/personalAgent \
--entrypoint main.py \
--authorizer-type CUSTOM_JWT \
--discovery-url $DISCOVERY_URL \
--allowed-clients $CLIENT_ID \
--framework strands \
--model-provider bedrock \
--language python \
--idle-timeout 120
```

Developers will find themselves asking "why do I have to delete the agent to only add it back again?"

Additionally, if I were to update a system prompt in my Strands main.py file provided by the scaffolding, `agentcore deploy -y` won't pick up that change

### Acceptance Criteria

- Change-detection support for agentcore deploy -y (and/or direct code deploy of the existing project files each time)
- Support for `agentcore configure` primitive (or alternative)

### Additional Context

_No response_