Support passing workload identity name to `require_access_token`

**Is your feature request related to a problem? Please describe.**
I want to use the 3LO flow with Identity outside of Runtime. As of now, this SDK falls back to the local auth settings expecting the `".agentcore.json"` which is not set by us. Hence, the SDK falls back to creating an Identity Workload but the agent's execution roles correctly gets an exception denied.

**Describe the solution you'd like**
I would like to use the decorator and pass the workload identity name. I would expect the decorator to get the workload access token and continue as is.

**Describe alternatives you've considered**
- Placing the `".agentcore.json"`
- Setting the `BedrockAgentCoreContext`

**Additional context**
Agent runs on Amazon ECS

Empieza por localizar la implementación en Python de `require_access_token` y la gestión de `.agentcore.json` y `BedrockAgentCoreContext` por parte del decorador. Traza cómo se seleccionan los tokens de acceso de workload para el caso de uso de ECS/3LO. Se considera terminado cuando el decorador acepta un nombre de identidad de workload y usa su token sin requerir ajustes de autenticación local.

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