Improve Alerts & Error UX

[prastut]

Alerts:

• Give user info that we only support file uploads less than 30MB.
• Give user info that we only support hevc format only (NetworkError when attempting to fetch resource. #19 (comment))

Error's:

• Provide errors if the user still bypasses the above alerts.
• Do them client side only, before sending the file to the Demux's gateway.

[prastut]

Hi @adamsoffer, is this something you could help us with in improving client-side UX?

Users are facing a lot of problems because the above UX isn't there, see their concerns below:

1. NetworkError when attempting to fetch resource. #19 (comment)
2. https://discord.com/channels/423160867534929930/426106677650128898/796295804087828531

Demux faces this problem as well inside Livepeer black box:

1. Hangs indefinitely in case of incompatible codec buidl-labs/Demux#30 (comment)

[adamsoffer]

Yes absolutely. Thanks for bringing this up.