Add emit_git_event() method to ChronicleClient that embeds a
GovernanceEnvelope in the CloudEvent data payload. The CloudEvent
id is set to the hex-encoded git_ref from the envelope.
Migrate GOV_COMMIT_CREATED, GOV_PUSH, and GOV_PR_CREATED in
git_commands.rs to use emit_git_event(). Non-git events continue
to use the existing emit() method.
Signed-off-by: Tyler King <tking@guildhouse.dev>
9a4eb378bf