Add android.noNotification for silent uploads

[elliottkember]

A consumer whose upload queue carries both user-visible media and housekeeping
payloads has no way to keep the housekeeping ones out of the notification shade.
Every upload posts a progress notification, because posting one is how the worker
enters foreground mode. In OpenSpace's app that means a field note syncing on
launch shows "Uploading Captures…", which reads to the user as a capture upload
stuck at 0%.

android: { noNotification: true } uploads a file without a notification. The
worker skips the channel registration, the foreground promotion and the notify
calls; nothing else about the upload changes. Default false.

The tradeoff, and why it is in the docs

The notification is the foreground service's notification, so a silent upload
runs as an ordinary background worker. The OS may defer it, or stop it mid-flight
for WorkManager to re-run later. That retry path already exists — a system stop
leaves the WorkManager row RUNNING and journals nothing, so JS never sees a
false terminal event. It does mean noNotification is wrong for anything that
takes real time to upload, so the option's doc comment, the README section and
the changelog all say to reserve it for small payloads.

Why an opt-out rather than showNotification

WorkManager persists this model as JSON, so a job enqueued by 8.0.0 can be run by
8.1.0 after an app upgrade. That JSON has no key for the new option, and Gson
leaves an absent Boolean field false — as an opt-out, absence means "notify",
so a replayed job keeps its notification and its foreground protection. As
showNotification it would have silently lost both. UploadTest covers exactly
this by stripping the key from serialized JSON.

The double negative stops at the model: the worker reads upload.showsNotification.

Progress accounting is unchanged

UploadProgress stays device-wide, so a visible notification's bar still counts
every in-flight upload, silent ones included. The bar reports what the device is
uploading, not what the notification is titled after; the README says so.

Verification

Ran locally: yarn typecheck, yarn lint:ci (3 pre-existing warnings in the
example app, 0 errors), yarn test (7 pass), and
./gradlew :react-native-background-upload:testDebugUnitTest — 29 tasks, all
green, with the 3 new UploadTest cases confirmed in the result XML.

Not verified on hardware. No device or emulator run, so the silent path has
not been observed end to end. Worth checking on an Android device before this is
relied on:

1. Start an upload with android: { noNotification: true }. Expect no
   notification, progress events still arriving, and a completed event.
2. Start one without the flag alongside it. Expect the usual notification, whose
   percentage moves for both uploads.
3. Background the app during a silent upload and confirm it still completes.

[elliottkember]

Opened against the wrong base repo; reopening on openspacelabs.