Support of CloudWatch format in vmisert

[tenmozes]

Is your feature request related to a problem? Please describe.
I'd like to have native support of Cloudwatch raw format to push data from it into VM or proxy which can do that

Describe alternatives you've considered
Use cloudwatch exporters or another one cloudwatch exporter

[valyala]

FYI, there are the following alternative exporters for CloudWatch metrics:

• https://github.com/prometheus/cloudwatch_exporter
• https://github.com/nerdswords/yet-another-cloudwatch-exporter