[OSD-12400] Collect Hosted Zones per Account

[mrWinston]

This PR implements the last part of OSD-12400, collecting the number of hosted zones per account.
It also parallelizes the collection of the RecordSetsPerHostedZone-metric, so it doesn't take forever.

Testing
first, make sure you're actually logged in to an aws account. Then run the following to disable the unneeded exporters

$ cat << EOF > ./aws-resource-exporter-config.yaml
rds:
  enabled: false
  regions:
    - "us-east-1"
vpc:
  enabled: false
  regions:
    - "us-east-1"
    - "eu-central-1"
  timeout: 30s
route53:
  enabled: true
  region: "us-east-1"
  timeout: 300s
  interval: 300s
ec2:
  enabled: false
  regions:
    - "us-west-1"
  timeout: 30s
EOF

# then, build & run the exporter:
$ go build
$ ./aws-resource-exporter

Wait until you see the message:

level=info ts=2022-08-31T13:49:06.561Z caller=route53.go:154 msg="Route53 metrics Updated"

on the console. This means, that all the r53 metrics have been collected and can now be retrieved from the cache.
In a separate shell window, run the following:

$ curl localhost:9115/metrics | grep "hostedzonesperaccount"

Make sure this prints out the newly implemented metrics, for example:

# HELP aws_resources_exporter_route53_hostedzonesperaccount_quota Quota for maximum number of Route53 hosted zones in an account
# TYPE aws_resources_exporter_route53_hostedzonesperaccount_quota gauge
aws_resources_exporter_route53_hostedzonesperaccount_quota 2000
# HELP aws_resources_exporter_route53_hostedzonesperaccount_total Number of Resource records
# TYPE aws_resources_exporter_route53_hostedzonesperaccount_total gauge
aws_resources_exporter_route53_hostedzonesperaccount_total 487