Make launcher run ID available in knapsack

[RebeccaMahany]

Launcher has a "run ID" that is currently added to all log messages. This run ID is only available inside the multislogger itself, and is created during new multislogger instantiation. We'd like to be able to access this run ID elsewhere, e.g. to report the current run ID up to k2 during startup, so we want to move it into launcher's knapsack. The instantiation of run ID inside multislogger.New also has the side effect that the same launcher run has multiple run IDs across different multisloggers -- for example, Windows event logs and debug.json logs will have different run IDs for the same run. Ideally, each time launcher runs, it should have a singular, unique run ID that it can access from the knapsack.

Notes for implementation:

• The run ID should be available in the knapsack so that launcher can e.g. report it up to k2 in the future
• The run ID should change if launcher reloads itself after an autoupdate (see IsLauncherReloadNeededErr, hereabouts), which means every call to runLauncher should get a new run ID
• The run ID should be applied to both the regular and system multislogger -- i.e., the run ID should be attached to all logs consistently, whether they are in the regular logs (debug.json) or the system logs (the Windows event logs on Windows, /var/log/kolide-k2/launcher-stderr.log on macOS, or journalctl logs on Linux)