[Hotfix] cleanup mr !324 mount vhostd dir correctly, enforce https for scrape jobs

mount vhost.d correctly on signalboost prod

• symptoms:
  • prometheus returning no data from signald scrape job
  • ngix logs show: 4132 no live upstreams while connecting to upstream, client: REDACTED, server: signald.signalboost.info
• suspected cause: metrics docker compose vhost.d ip whitelisting works because we mount a volume from the filesystem instead of using a named volume, but in signalboost prod configs we still use a (vestigal) named volume from example configs
• attemped fix: mount the vhost.d directory from the repo instead of using the named volume

specify https scheme in prometheus_prod.yml configs

• this fixes a longstanding unnoticed bug in which we shipped our prometheus scrape job configs to use the default scheme (which is http) instead of explicitly specifying https