aws-for-fluent-bit: logGroupTemplate default value

**Describe the bug**
I'm switching to the new cloudwatch_logs plugin and having a hard time with the logGroupTemplate setting. I have cloudWatchLogs.autoCreateGroup set to false and I've specified the logGroupName, however the logGroupTemplate value is listed as optional in the documentation but the default value conflicts with my logGroupName setting. To workaround this issue I just set the logGroupTemplate value to a blank string.

**Steps to reproduce**
Set values to this:

cloudWatchLogs:
enabled: true
autoCreateGroup: false
logGroupName: "/aws/eks/mycluster/workloads"
region: us-east-2

**Expected outcome**
Expected logs in Cloudwatch at "/aws/eks/mycluster/workloads", however got IAM errors about "/aws/eks/fluentbit-cloudwatch/workload/..."

**Environment**

* Chart name: aws-for-fluent-bit
* Chart version: 0.1.24
* Kubernetes version: 1.24
* Using EKS (yes/no), if so version? yes, 1.24

**Additional Context**:

Start with the aws-for-fluent-bit chart's cloudWatchLogs configuration and trace how logGroupTemplate gets its default when logGroupName is set. Reproduce the values from the issue with autoCreateGroup disabled, then verify that rendered configuration targets /aws/eks/mycluster/workloads without the conflicting fluentbit-cloudwatch path.

Written by the indexing model from the issue text.