start-stop-mwaa-environment - AWS_REGION env var needed to deploy outside of us-east-1

Hello guys,
I was testing the `start-stop-mwaa-environment` project for our MWAA in `eu-west-3`.
I just wanted to let you know, that at least in my case, to successfully run the `npm run deploy` step I had to set this env var:
```
export AWS_REGION=eu-west-3
```

Without this variable `npm run deploy` would output this warning (see the `-us-east-1`):
```
current credentials could not be used to assume 'arn:aws:iam::*****:role/cdk-hnb659fds-deploy-role-*****-us-east-1', but are for the right account. Proceeding anyway.
```
And then errors out with:
```
mwaa-pause-resume-airflow-internal: SSM parameter /cdk-bootstrap/hnb659fds/version not found. Has the environment been bootstrapped? Please run 'cdk bootstrap' (see https://docs.aws.amazon.com/cdk/latest/guide/bootstrapping.html)
```

After setting:
```
export AWS_REGION=eu-west-3
```
It worked perfectly.
Maybe is something that will be useful to have in the readme.

We are on airflow `2.7.2` and I am using the latest code of this project available in `main`.