…trollers-k8s#341)

Issue #, if available:

[1330](aws-controllers-k8s/community#1330)

Description of changes:

In the [documentation on using a shared credentials file](https://aws-controllers-k8s.github.io/community/docs/user-docs/authentication/#use-a-shared-credentials-file) there are instructions for mounting a secret containing AWS credentials on the pod for an ACK controller, so it can use those credentials. However, for this controller there is no way to specify which secret to use when following the [installation instructions with Helm](https://aws-controllers-k8s.github.io/community/docs/tutorials/rds-example/#install-the-ack-service-controller-for-rds). This change adds new values settings that can be used to specify that secret. 

## Manual testing

- Render template

```bash
# Generate helm chart
cd aws-controllers-k8s/code-generator
./scripts/build-controller-release.sh rds

# Render template 
cd aws-controllers-k8s/rds-controller
# new volume, volume mount, and env vars are visible
helm -n testns template rds-ack helm/ --debug \
   --set aws.credentials.secretName=aws-creds \
   --set aws.credentials.profile=ack > render_with_secret.yaml
# no new stuff is visible
helm -n testns template rds-ack helm/ --debug  > render_without_secret.yaml
```

- Deploy to minikube: 

```bash
# Create secret with AWS credential as described in https://aws-controllers-k8s.github.io/community/docs/user-docs/authentication/#use-a-shared-credentials-file
## Assuming AWS_SHARED_CREDENTIALS_FILE is properly set
CREDS_CONTENT=$(cat ${AWS_SHARED_CREDENTIALS_FILE} | sed 's/^/    /';)
kubectl create namespace testns
kubectl -n testns apply -f - <<EOF
apiVersion: v1
kind: Secret
metadata:
  name: aws-creds
type: Opaque
stringData:
  credentials: |
$CREDS_CONTENT
EOF

# Install chart as in https://aws-controllers-k8s.github.io/community/docs/tutorials/rds-example/#install-the-ack-service-controller-for-rds
# Without new values setting, the controller fails to find the credentials 
helm -n testns install rds-ack helm/ --set=aws.region=us-east-1 
$ kubectl -n testns logs -f -l "app.kubernetes.io/instance=rds-ack"
1.6552236370473711e+09  ERROR   setup   Unable to create controller manager     {"aws.service": "rds", "error": "unable to determine account ID: unable to get caller identity: NoCredentialProviders: no valid providers in chain. Deprecated.\n\tFor verbose messaging see aws.Config.CredentialsChainVerboseErrors"}

# Using the additional values settings it is able to get the credentials
helm -n testns upgrade rds-ack helm/ \
   --set=aws.region=us-east-1 \
   --set aws.credentials.secretName=aws-creds \
   --set aws.credentials.profile=ack
$ kubectl -n testns logs -f -l "app.kubernetes.io/instance=rds-ack"
1.655223683774505e+09   INFO    controller.globalcluster        Starting EventSource    {"reconciler group": "rds.services.k8s.aws", "reconciler kind": "GlobalCluster", "source": "kind source: *v1alpha1.GlobalCluster"}
...
```


By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.