Save assets pack not computing the progress correctly

The [function in charge of updating the progress of saving the assets](https://github.com/decentraland/builder/blob/1b7e26d6d889eaa1aaf21fa7197477a43106af8f/src/modules/assetPack/sagas.ts#L31) is executed once and then, [its result](https://github.com/decentraland/builder/blob/1b7e26d6d889eaa1aaf21fa7197477a43106af8f/src/modules/assetPack/sagas.ts#L74) is used as a function to be executed [after an asset it loaded](https://github.com/decentraland/builder/blob/1b7e26d6d889eaa1aaf21fa7197477a43106af8f/src/modules/assetPack/sagas.ts#L75). As the function is executed with the total values of items once, executing it again as a promise won't work.

Fix this procedure to make the progress be updated as it should be.

Start in src/modules/assetPack/sagas.ts at the progress updater around lines 31, 74, and 75. Trace how the updater result is passed after each asset is loaded, then verify that progress is recalculated and updated for each asset rather than computed only once.

Written by the indexing model from the issue text.