🚧 feat(Mobile): Use client side hash to check if asset exists in remote before backup

[dramikei]

Allows Client to check for asset existence in remote server by making use of asset SHA-1 checksum along with API implemented in #2072

Fixes #1553

Problem statement:

When reinstalling immich app, or when asset backup already exists on immich server (through icloudpd and immich-cli for example) the client app uploads all the assets from the device which then get deduplicated from the server-side. Resulting in unnecessary upload of 20k+ assets, wasted bandwidth and time.

Change:

Assets that are already on the server are ignored and not uploaded to the server

Tests:

• Tested on Android (emulator)
• Tested on iOS (physical device)

[dramikei]

Found some issues while testing on iOS:

1. Hashing a large amount of files takes quite some time, so its better to convert hashing before backup into a cancellable "job" of its own with persistence in case app gets killed
2. If we have assets uploaded to icloud with Optimize storage turned on, the hashing function sometimes fails to fetch the original file because of final file = await assetEntities[i].originFile; in hash service. converting this to final file = await assetEntities[i].loadFile(withSubtype: Platform.isIOS); seems to fix the issue, but raises another concern (see point 3)
3. when using loadFile PhotoManagerPlugin downloads each asset to hash, which slows down the entire backup preparation.

[nmschulte]

Suggested change

	id: e.localId != null ? e.localId! : e.id.toString()))
	id: e.localId ?? e.id.toString()))