Add metrics exporter for AWS quota service.

[jeschkies]

Inspired by https://github.com/mulesoft-labs/awslimitchecker and enhanced metrics this adds support for exporting quota metrics. These include _limit and _usage metrics for different services and instances.

Here is an example output:

aws_ec2_quota_running_on_demand_standard_instances_limit{region="us-east-1",account_id="integration-test"} 1152
aws_ec2_quota_running_on_demand_standard_instances_usage{region="us-east-1",account_id="integration-test"} 8
aws_ec2_quota_running_on_demand_f_instances_limit{region="us-east-1",account_id="integration-test"} 128
aws_ec2_quota_running_on_demand_f_instances_usage{region="us-east-1",account_id="integration-test"} 0
aws_ec2_quota_running_on_demand_g_and_vt_instances_limit{region="us-east-1",account_id="integration-test"} 768
aws_ec2_quota_running_on_demand_g_and_vt_instances_usage{region="us-east-1",account_id="integration-test"} 0
aws_ec2_quota_running_on_demand_inf_instances_limit{region="us-east-1",account_id="integration-test"} 128
aws_ec2_quota_running_on_demand_inf_instances_usage{region="us-east-1",account_id="integration-test"} 0
aws_ec2_quota_running_on_demand_p_instances_limit{region="us-east-1",account_id="integration-test"} 768
aws_ec2_quota_running_on_demand_p_instances_usage{region="us-east-1",account_id="integration-test"} 0
aws_ec2_quota_running_on_demand_x_instances_limit{region="us-east-1",account_id="integration-test"} 128
aws_ec2_quota_running_on_demand_x_instances_usage{region="us-east-1",account_id="integration-test"} 0
aws_ec2_quota_ec2_vpc_elastic_ips_limit{account_id="integration-test",region="us-east-1"} 5
aws_ec2_quota_ec2_vpc_elastic_ips_usage{region="us-east-1",account_id="integration-test"} 7
aws_elasticache_quota_nodes_per_region_limit{region="us-east-1",account_id="integration-test"} 300
aws_elasticache_quota_nodes_per_region_usage{region="us-east-1",account_id="integration-test"} 0