This removes the proguard rules (no longer required) and
adds a link to discover the custom.md file.

Fixes #2673.

This PR protects against the initial `NullPointerException` ever happening.

This is a rare case, and we do not have anything to go on at this point, so we fallback to a new intent, and the user is routed to the home activity.

This changes glean internals so that recording right before
a call to `sendPings` puts the data in that ping. In order
to sanely allow this, `sendPings` now returns a Deferred
which can be used to check if the ping was correctly taken
care of.
This additionally introduces a function to wait for WorkManager
jobs to be queued (in tests) and an `async` facility in Dispatchers.kt

This adds the first command, "updateExperiments" that will force the ExperimentsUpdater to update immediately.

- Adds doc section to README.md
- Adds export statement to AndroidManifest.xml
- Init Logger with a TAG more in line with how the rest of the component uses Logger
- Fix an issue that was preventing the debug activity from working correctly since it was attempting to do networking on main thread.  Had to use a coroutine to perform the update in the background.

Use WorkManager along with a PeriodicWorkRequest to update experiments every 6 hours.