Enhancements and Bug fixes to the Lambda Stats

[christus02]

Below enhancements were done to the existing Lambda function:

• Using a Template based approach to pull stats from Citrix ADC (similar to citrix metrics exporter metrics.json). Based on a JSON file, we extract Nitro stats from Citrix ADC
• This Metrics JSON would also act as a template for Cloud Watch Metrics so that creating a data structure for CloudWatch metrics is mostly avoided in the Script
• The Plan is have multiple metrics JSON for different monitoring tools like Datadog, Google Operations, etc so that script becomes generic. I have also created a tool that automatically creates a metrics.json for CloudWatch and other monitoring tools (https://github.com/christus02/citrix-adc-metrics-exporter-serverless/blob/master/utils/metrics-template-creator/metrics-template-creator.py)
• Added few more dimensions in the CloudWatch data structure
• Selective feature checklist - even though the metrics.json has all the nitro features, we can fine tune what stats to be pulled and pushed using a list.
• Extracting Nitro stats via public IP of the VPX (if available).
• Few other modifications in the CloudWatch upload metrics function.
• Generalised the Nitro get_stats function
• Few other bug fixes to suit to the latest AWS Lambda changes (both in code and in Makefile)