Add Ubuntu Pro Updates exporter to the exporters list

[B0go]

Adds ubuntu_pro_updates_exporter to the Miscellaneous third-party exporters.

It exposes Ubuntu package update status through the Ubuntu Pro client's machine-readable API: pending updates by pocket and status (including security fixes only available via ESM), reboot-required state, installed-package origins, and CVE exposure. Port 10052 is registered on the default port allocations wiki page. MIT licensed, released binaries, in production use across a ~2k host fleet.

cc @RichiH

Representative sample output

ubuntu_pro_updates_exporter_up 1
ubuntu_pro_updates_attached 0
ubuntu_pro_updates_client_info{version="37.2ubuntu~22.04.1"} 1
ubuntu_pro_updates_pending{pocket="standard-security",status="upgrade_available"} 54
ubuntu_pro_updates_pending{pocket="standard-security",status="upgrade_available_not_preferred"} 1
ubuntu_pro_updates_pending{pocket="standard-updates",status="upgrade_available"} 9
ubuntu_pro_updates_reboot_required{state="no"} 1
ubuntu_pro_updates_download_bytes{pocket="standard-security"} 2.546073e+07
ubuntu_pro_updates_installed_packages{origin="main"} 176
ubuntu_pro_updates_cves{fix_status="fixed",priority="high"} 3
ubuntu_pro_updates_cves{fix_status="fixed",priority="medium"} 116
ubuntu_pro_updates_cves{fix_status="vulnerable",priority="medium"} 89
ubuntu_pro_updates_cve_fixes{origin="security"} 116
ubuntu_pro_updates_cve_fixes{origin="updates"} 182
ubuntu_pro_updates_exporter_last_success_timestamp_seconds 1.789050262e+09