Overwrite existing CloudWatch config if merging config fails

`append-config` merges config, but fails when there are conflicting parameters:
```
    2024/08/07 19:45:32 Under path : /metrics/metrics_collected/mem | Error : Different values are specified for mem
    2024/08/07 19:45:32 Under path : /metrics/metrics_collected/disk | Error : Different values are specified for disk
    2024/08/07 19:45:32 Under path : /metrics/append_dimensions | Error : Different values are specified for append_dimensions
    2024/08/07 19:45:32 Under path : /metrics/metrics_collected/mem | Error : Different values are specified for mem
    2024/08/07 19:45:32 Under path : /metrics/metrics_collected/disk | Error : Different values are specified for disk
    2024/08/07 19:45:32 Under path : /metrics/append_dimensions | Error : Different values are specified for append_dimensions
```

`fetch-config` overwrites config.

This commit makes the code to try merging the config first. If it fails, overwrite the config.

Signed-off-by: Hanwen <[email protected]>

Author: hanwen-cluster

cookbooks/aws-parallelcluster-environment/resources/cloudwatch/partial/_cloudwatch_common.rb

@@ -175,6 +175,6 @@ def package_path
   execute "cloudwatch-agent-start" do
     user 'root'
     timeout 300
-    command "/opt/aws/amazon-cloudwatch-agent/bin/amazon-cloudwatch-agent-ctl -a append-config -m ec2 -c file:/opt/aws/amazon-cloudwatch-agent/etc/amazon-cloudwatch-agent.json -s"
+    command "/opt/aws/amazon-cloudwatch-agent/bin/amazon-cloudwatch-agent-ctl -a append-config -m ec2 -c file:/opt/aws/amazon-cloudwatch-agent/etc/amazon-cloudwatch-agent.json -s || /opt/aws/amazon-cloudwatch-agent/bin/amazon-cloudwatch-agent-ctl -a fetch-config -m ec2 -c file:/opt/aws/amazon-cloudwatch-agent/etc/amazon-cloudwatch-agent.json -s"
   end unless node['cluster']['cw_logging_enabled'] != 'true' || on_docker?
 end

cookbooks/aws-parallelcluster-environment/spec/unit/resources/cloudwatch_spec.rb

@@ -255,7 +255,7 @@ def self.configure(chef_run)
           is_expected.to run_execute("cloudwatch-agent-start").with(
             user: 'root',
             timeout: 300,
-            command: "/opt/aws/amazon-cloudwatch-agent/bin/amazon-cloudwatch-agent-ctl -a append-config -m ec2 -c file:/opt/aws/amazon-cloudwatch-agent/etc/amazon-cloudwatch-agent.json -s"
+            command: "/opt/aws/amazon-cloudwatch-agent/bin/amazon-cloudwatch-agent-ctl -a append-config -m ec2 -c file:/opt/aws/amazon-cloudwatch-agent/etc/amazon-cloudwatch-agent.json -s || /opt/aws/amazon-cloudwatch-agent/bin/amazon-cloudwatch-agent-ctl -a fetch-config -m ec2 -c file:/opt/aws/amazon-cloudwatch-agent/etc/amazon-cloudwatch-agent.json -s"
           )
         end
       end
@@ -313,7 +313,7 @@ def self.configure(chef_run)
           is_expected.to run_execute("cloudwatch-agent-start").with(
             user: 'root',
             timeout: 300,
-            command: "/opt/aws/amazon-cloudwatch-agent/bin/amazon-cloudwatch-agent-ctl -a append-config -m ec2 -c file:/opt/aws/amazon-cloudwatch-agent/etc/amazon-cloudwatch-agent.json -s"
+            command: "/opt/aws/amazon-cloudwatch-agent/bin/amazon-cloudwatch-agent-ctl -a append-config -m ec2 -c file:/opt/aws/amazon-cloudwatch-agent/etc/amazon-cloudwatch-agent.json -s || /opt/aws/amazon-cloudwatch-agent/bin/amazon-cloudwatch-agent-ctl -a fetch-config -m ec2 -c file:/opt/aws/amazon-cloudwatch-agent/etc/amazon-cloudwatch-agent.json -s"
           )
         end
       end