Allow configuring the local host for port forwarrding sessions - #2

The port forwarding host is hardcoded to be localhost. This prevents us from connecting to it directly from docker using host.docker.internal.
Allow configuring the local host name using  `SSM_PLUGIN_LOCAL_HOST`.

Example:
```sh
export SSM_PLUGIN_LOCAL_HOST="0.0.0.0"
aws ssm start-session \
  --region ap-southeast-2 \
  --target [BASTION_EC2_INSTANCE_ID] \
  --document-name AWS-StartPortForwardingSessionToRemoteHost \
  --parameters host="[RDS_PG_ENDPOINT]",portNumber="5432",localPortNumber="2222"
```

Test:
```sh
docker run -it --rm  \
  --add-host "host.docker.internal:host-gateway" \
  -e "PGPASSWORD" \
  postgres:16.3 psql -h host.docker.internal -p 2222 -U [DB_USER] -d [DB_NAME]

```
aws#14 (comment)