Dev: use build product flavors for app store release (#1205)

## Description
Instead of applying a code patch, this PR uses build time [product
flavors](https://developer.android.com/build/build-variants#product-flavors)
to define the existing default and an app store variant. This is more
robust than maintaining a patch file and making sure it is applied
before building.

The app store variant applies the same code changes (removing install
permission, requiring leanback, & setting `UpdateChecker.ACTIVE`), but
via manifest placeholders/merging and `BuildConfig` entries.

There are no user facing changes.

### Related issues
None

### Testing
Built the variants and verified manifest changes via aapt

## Screenshots
N/A

## AI or LLM usage
None

app/src/main/java/com/github/damontecres/wholphin/services/UpdateChecker.kt

@@ -65,7 +65,7 @@ class UpdateChecker
 
             private val NOTE_REGEX = Regex("<!-- app-note:(.+) -->")
 
-            val ACTIVE = true
+            const val ACTIVE = BuildConfig.UPDATING_ENABLED
         }
 
         /**