chore(mobile): add toast notification for "Download Started"

[DeadEnded]

Recently started self hosting Immich and using the mobile Android app (fantastic work being done by the way!). We recently noticed that when we started a download in the app - nothing happened. Downloading large files (long videos) gave no feedback until the download was completed.

So, I have made an attempt to add a toast notification at the start of the download to signal that the download did indeed start so the user has confirmation that they initiated the download. I have Google Translated as many of the languages as I felt comfortable with the results of. If I should remove these and let a native speaker do their languages translations (so nothing is mistranslated into something inappropriate) please let me know.

I am a novice, but very much appreciate the projects I use and contribute when I can. Please let me know if anything needs changed/fixed/removed, etc. and I'm happy to do the work!

Thank you - Cheers! DeadEnd

[alextran1502]

Thank you for your contribution, you will only need to add the translation string to en-US.json file for future reference