bug: `secretsmanager` backend does not support AWS managed secrets

[tmeijn]

See: https://docs.aws.amazon.com/secretsmanager/latest/userguide/service-linked-secrets.html

Secrets created by AWS use the <SERVICE>! prefix. However when trying to retrieve such a secret with chamber we get the following error:

chamber -b secretsmanager env rds!cluster-1a96bebc-86c1-4982-9f9f
Error: Failed to validate service: Failed to validate service name 'rds!cluster-1a96bebc-86c1-4982-9f9f-7d6a651d2464'. Only alphanumeric, dashes, forward slashes, full stops and underscores are allowed for service names. Service names must not start or end with a forward slash

I think this occurs because it uses the same validation as SSM backend.