Add `crates-io-heroku-metrics` under automation

[Kobzol]

Repo: https://github.com/rust-lang/crates-io-heroku-metrics

Extracted from GH:

org = "rust-lang"
name = "crates-io-heroku-metrics"
description = "Heroku metrics collector for crates.io"
bots = []

[access.teams]
infra = "maintain"
security = "pull"

[access.individuals]
rylev = "admin"
Mark-Simulacrum = "admin"
pietroalbini = "admin"
kennytm = "maintain"
rust-lang-owner = "admin"
badboy = "admin"
shepmaster = "maintain"
jdno = "admin"
Kobzol = "maintain"

[Turbo87]

I actually have no idea. @pietroalbini might know more about this since I think he set this up originally.

[pietroalbini]

This is a live repository that must not be archived. It powers the Grafana dashboard for crates.io.

[pietroalbini]

More context on what the repository does: https://rust-lang.zulipchat.com/#narrow/stream/318791-t-crates-io/topic/crates-io-heroku-metrics

[Kobzol]

Thank you for the context! Turned it into a normal repository.