Feature : Download Metrics for rawdataapi

[kshitijrajsharma]

What does this PR do ?

• Adds optional endpoints that can be enabled through env variable for the metrics endpoint which should allow people to download the stats , such as total downloads per day , total unique users per day etc
• Currently only available to admin users

How to test ?

• Enable this feature with ENABLE_METRICS_APIS env variable and you should see this endpoint
  

Consideration

In order to fetch the total download stats raw-data-api currently depends upon setup of https://github.com/hotosm/s3-logs-analyzer/ manually so that it can populate the stats on metrics table daily . Which is available here : https://github.com/hotosm/s3-logs-analyzer/blob/master/ops/systemd/download_metrics.service