Simplify and separate W3ACT AirFlow tasks

[anjackson]

Currently, one file contains three workflows, because they share code for dumping the W3ACT DB, and each runs their own dump in case of conflicts due to workflows running simultaniously. To me a bit more canonical-Airflow in style and a bit easier to manage, the workflows could be changed as follows:

• For w3act_export
  • This runs hourly, to keep access services up to date. As it's the most frequent, this is the one that should export W3ACT data.
  • Rather than maintaining a single folder and replacing, we should use a shared per-run folder, like /var/tmp/w3act_export_2021-12-10T09:00:00Z/ so that each run get's it's own output folder.
  • These will get cleaned up automatically every 30 days by the OS.
• For w3act_backup and w3act_report
  • These would use Airflows ExternalTaskSensor to await the completion of the w3act_export workflow for the hour at which they run, e.g. 2021-12-10T00:00:00Z. They would then refer to the corresponding W3ACT DB dump and use that instead of a separate dump.

This would make it easier to keep them in separate files, which is also more canonical for Airflow, and makes things a bit easier to understand.

[anjackson]

Note in particular that having launch-this-crawl tasks and update-this-access-service tasks tied together is not a great idea. e.g. on DEV when we want to try one without running the other.

[anjackson]

I've separated out the crawl launcher, and I think that's good enough for now. Note that using things like External Task etc. don't really help because it means e.g. the launcher can't run because the other one didn't. Instead, it makes sense for them to be separate and for the launch source files to be atomically updated.