Support SSM (Systems Manager) parameters

**Describe the enhancement:**
There are two ways to store secrets in AWS:
- [AWS Secrets-Manager](https://aws.amazon.com/de/secrets-manager/)
- [SSM parameter store](https://docs.aws.amazon.com/systems-manager/latest/userguide/systems-manager-parameter-store.html)

Currently, only aws secrets are supported:
[config.yaml](https://www.elastic.co/guide/en/esf/current/aws-elastic-serverless-forwarder-configuration.html#use-secrets-manager)
[Deployment](https://www.elastic.co/guide/en/esf/current/aws-deploy-elastic-serverless-forwarder.html#_general_configuration)

Even though the docu only mentions secrets manager, the name of the parameter `ElasticServerlessForwarderSSMSecrets` gives the impression that SSM is suppored as well, what seems not to be the case.

It would be very helpful to additionally support ssm parameters as well.

**Describe a specific use case for the enhancement or feature:**
Using credentials stored in ssm parameter store instead of sectets manager

**Config example/proposal**

Deployment:
```
parameter:
ElasticServerlessForwarderSSMParameters: ["arn:aws:ssm:eu-central-1:123456:parameter/es_url"]
```
config.yaml:
```
inputs:
- type: "s3-sqs"
id: "arn:aws:sqs:%REGION%:%ACCOUNT%:%QUEUENAME%"
outputs:
- type: "elasticsearch"
args:
elasticsearch_url: "arn:aws:ssm:eu-central-1:123456789:parameter:es_url"
```

Start by locating the existing AWS Secrets Manager handling described in config.yaml and the Deployment documentation. Compare the proposed ElasticServerlessForwarderSSMParameters setting and SSM ARN format with the current configuration path. Done means credentials can be read from AWS SSM Parameter Store and the configuration and deployment documentation accurately describe the supported setup.

Written by the indexing model from the issue text.