Integrate with the metrics API

[smashwilson]

Once atom/telemetry is integrated into Atom (atom/telemetry#8), consume the metrics package service and send "interesting metrics" to GitHub's internal metrics pipeline for users who have consented to it.

We'll need to decide on what metrics we want to collect initially - I believe @annthurium had identified some in their original write-up. If we can think of any other hypotheses we want to test in our initial ship, though, this would be a good opportunity to get them in early.

#1545 will help lay some of the groundwork for this, I think.

/cc @telliott27 for awareness.

[annthurium]

here's what we came up with during the editor tools mini summit:

• Commits made by the GitHub package
• Commits made by the GitHub package that have a co author
• Authentication requests made for the GitHub package
• GitHub package version
• Amend actions
• Partial staging actions
• opening/closing the Git / GitHub panes
• Push actions
• pull actions
• create pull request actions

I'm sure there are more things we could track, though!