Add http download failure metric

[rwxzhu]

Add a http download failure metric emission to the deploy-agent.

Tested on devapp by running

> IS_PINTEREST=true METRIC_PORT_HEALTH=18126 METRIC_CACHE_PATH=/mnt/deployd/metrics.cache /home/ruizhu/code/teletraan/deploy-agent/bazel-bin/deployd/deploy-downloader -f /etc/deployagent.conf -v nonexistant_aa874a6 -u https://deployrepo.pinadmin.com/deploy-agent-pex/non_existant-aa874a6.tar.gz -e deploy-init
2024-03-07 03:53:30,000:INFO: Start to download the package.
2024-03-07 03:53:30,000:INFO: Start to download from url https://deployrepo.pinadmin.com/deploy-agent-pex/non_existant-aa874a6.tar.gz to /mnt/builds/deploy-init-nonexistant_aa874a6.tar.gz
2024-03-07 03:53:30,000:INFO: Running command: curl -o /mnt/builds/deploy-init-nonexistant_aa874a6.tar.gz -fksS https://deployrepo.pinadmin.com/deploy-agent-pex/non_existant-aa874a6.tar.gz
2024-03-07 03:53:30,070:INFO: [0.07]curl: (22) The requested URL returned error: 404 Not Found
2024-03-07 03:53:30,070:INFO: Finish downloading: https://deployrepo.pinadmin.com/deploy-agent-pex/non_existant-aa874a6.tar.gz to /mnt/builds/deploy-init-nonexistant_aa874a6.tar.gz
2024-03-07 03:53:30,070:ERROR: Failed to download the tar ball for /mnt/builds/deploy-init-nonexistant_aa874a6.tar.gz
2024-03-07 03:53:30,070:ERROR: Download failed.

metric being populated