cmd/worklog: provide cross-host data api for dashboard

[kortschak]

If a user works across a number of hosts it can be difficult to construct a summary of total time worked since more than one host may be active at the same time (for example if one host is used as a barrier server, it will always be active while work may be happening on a barrier client). To address this a8f3431 added support for obtaining raw unsummarised events over a period.

This raw data can be used from multiple sources to construct a dashboard for this case, at least for AFK time, transition graphs and application flow are more difficult and may require separated treatment; this would be either completely separate panels in the dashboard, host-labelled components in shared panels (likely only for transition graphs), or non-handling of remote host data in these cases — most likely in the first instance.

The platform-specific behaviour of hosts further complicates these two data sources; in the case of a barrier set-up, MacOS does not take focus away from windows when the host is not the active host due to its unfortunate application-based (rather than window-based) UI design (maybe watcher can be taught to deal with this).

Minumum required:

• raw data endpoint
• allow mTLS communication between client summary aggregator and remote raw data source (requires addition of separate raw data server if this is turned on)
• configuration of external raw data sources
• hook raw data GET query into eventData method

Similar additions are needed for a cross-host summary end point:

• raw summary endpoint
• hook raw summary data GET query into rangeSummary method