Amazon Cloudwatch Agent Does Not Use Credential File for Inputs: Prometheus Scraper Configuration

# Bug Report

The CloudWatch agent does not appear to utilize the file named `/root/.aws/credentials` as a credential source. The logs below show that the credential file _is_ being used for "outputs" configuration but is not being used by some number of "inputs" configurations in particular `[inputs.prometheus_scraper.ecs_service_discovery.service_name_list_for_tasks]`.

Evidence of credential file being used by "output" - from the logs you can see `shared_credential_file` is set to `shared_credential_file = "/root/.aws/credentials"`.

```
[outputs]

[[outputs.cloudwatchlogs]]
force_flush_interval = "5s"
log_stream_name = "7eccfaad73e7"
profile = "AmazonCloudWatchAgent"
region = "us-west-2"
shared_credential_file = "/root/.aws/credentials"
tagexclude = ["metricPath"]
[outputs.cloudwatchlogs.tagpass]
metricPath = ["logs"]
```

And evidence that the file is _not_ being used by inputs despite being available:

From the logs you can see no evidence that `shared_credential_file = "/root/.aws/credentials"` is used.
```
[inputs]

[[inputs.prometheus_scraper]]
cluster_name = "test"
prometheus_config_path = "/etc/cwagentprometheusconfig/prometheus.yaml"
[inputs.prometheus_scraper.ecs_service_discovery]
sd_cluster_region = "us-west-2"
sd_frequency = "1m"
sd_result_file = "/tmp/cwagent_ecs_auto_sd.yaml"
sd_target_cluster = "ecs-prometheus"

[[inputs.prometheus_scraper.ecs_service_discovery.service_name_list_for_tasks]]
sd_job_name = "prometheus-exporter"
sd_metrics_path = "/metrics"
sd_metrics_ports = "5000"
sd_service_name_pattern = "prometheus-exporter"
[inputs.prometheus_scraper.tags]
log_group_name = "prometheus"
metricPath = "logs"
```

and further:

```
ts=2023-04-22T18:35:02.503Z caller=start.go:325 level=info msg="Add extra relabel_configs and metric_relabel_configs to save job, instance and __name__ before user relabel"
ts=2023-04-22T18:35:02.503Z caller=start.go:342 level=info msg="Completed loading of configuration file" filename=/etc/cwagentprometheusconfig/prometheus.yaml
ts=2023-04-22T18:35:02.503Z caller=start.go:246 level=info msg="finish handling config file"
ts=2023-04-22T18:35:02.503Z caller=start.go:183 level=info msg="start discovery"
2023-04-22T18:35:03Z E! Failed to get credential from session: NoCredentialProviders: no valid providers in chain
caused by: EnvAccessKeyNotFound: failed to find credentials in the environment.
SharedCredsLoad: failed to load profile, .
EC2RoleRequestError: no EC2 instance role found
caused by: RequestError: send request failed
caused by: Get "http://169.254.169.254/latest/meta-data/iam/security-credentials/": dial tcp 169.254.169.254:80: connect: connection refused
2023-04-22T18:35:03Z D! [logagent] open file count, 0
```

# Reproduction

To reproduce the error use the files contained within the "Config" section below.

# Expected Output

The credentials from the credentials file should be used.

# Actual Output

I saw the following errors followed by an application exit:

```
ts=2023-04-22T18:35:02.503Z caller=start.go:325 level=info msg="Add extra relabel_configs and metric_relabel_configs to save job, instance and __name__ before user relabel"
ts=2023-04-22T18:35:02.503Z caller=start.go:342 level=info msg="Completed loading of configuration file" filename=/etc/cwagentprometheusconfig/prometheus.yaml
ts=2023-04-22T18:35:02.503Z caller=start.go:246 level=info msg="finish handling config file"
ts=2023-04-22T18:35:02.503Z caller=start.go:183 level=info msg="start discovery"
2023-04-22T18:35:03Z E! Failed to get credential from session: NoCredentialProviders: no valid providers in chain
caused by: EnvAccessKeyNotFound: failed to find credentials in the environment.
SharedCredsLoad: failed to load profile, .
EC2RoleRequestError: no EC2 instance role found
caused by: RequestError: send request failed
caused by: Get "http://169.254.169.254/latest/meta-data/iam/security-credentials/": dial tcp 169.254.169.254:80: connect: connection refused
2023-04-22T18:35:03Z D! [logagent] open file count, 0
```

# Version

`AmazonCloudWatchAgent 1.247358.0`

# Config

Configuration to reproduce this setup is below:

## docker-compose.yml

```
services:
cloudwatch-agent:
image: public.ecr.aws/cloudwatch-agent/cloudwatch-agent:latest
volumes:
- $HOME/.aws/credentials:/root/.aws/credentials:ro
- ./cloudwatch-agent/amazon-cloudwatch-agent-prometheus.json:/etc/cwagentconfig/config.json
- ./cloudwatch-agent/prometheus.yaml:/etc/cwagentprometheusconfig/prometheus.yaml
```

## amazon-cloudwatch-agent-prometheus.json

```
{
"agent":{
"debug": true,
"logfile": "",
"metrics_collection_interval":10
},
"logs":{
"metrics_collected":{
"prometheus":{
"ecs_service_discovery": {
"sd_cluster_region": "us-west-2",
"sd_frequency": "1m",
"sd_result_file": "/tmp/cwagent_ecs_auto_sd.yaml",
"sd_target_cluster": "ecs-prometheus",
"service_name_list_for_tasks": [
{
"sd_job_name": "prometheus-exporter",
"sd_metrics_path": "/metrics",
"sd_metrics_ports": "5000",
"sd_service_name_pattern": "prometheus-exporter"
}
]
},
"cluster_name": "test",
"log_group_name":"prometheus",
"prometheus_config_path":"/etc/cwagentprometheusconfig/prometheus.yaml"
}
}
}
}
```

## prometheus.yaml

```
global:
scrape_interval: 1m
scrape_timeout: 10s
scrape_configs:
- job_name: prometheus-exporter
metrics_path: /metrics
scheme: http
file_sd_configs:
- files:
- /tmp/cwagent_ecs_auto_sd.yaml
```

# Environment

I am using the Docker Image `public.ecr.aws/cloudwatch-agent/cloudwatch-agent:latest` - which, at this moment, contains CloudWatch agent `1.247358.0`.

# Additional Context

None.

Start by reproducing the failure with docker-compose.yml, amazon-cloudwatch-agent-prometheus.json, and prometheus.yaml using the mounted /root/.aws/credentials file. Trace the ECS service discovery configuration and credential loading shown in the logs; done means the Prometheus scraper's ECS discovery uses the configured credential file instead of exiting with NoCredentialProviders.

Written by the indexing model from the issue text.