New asset commands

[sergey-borovkov]

What does this PR do?

Supports inject-js and set-headers commands for web assets.
Inject-js allows setting JS injection code for web assets. Injected code will be executed during playback on the device once the asset is loaded.

set-headers similarly works on web assets setting values of custom HTTP headers.
Usage is a bit awkward but I did not come up with better syntax:
screenly asset set-headers 01FJVFP0QVD1E5TA70SA66AJPF --header k=v --header k2=v2

Also adds basic-auth command that allows setting the basic auth header by accepting username and password.

GitHub issue or Phabricator ticket number?

T6482

How has this been tested?

New unit tests + manual use.

Checklist before merging

• If have added tests.
• Is this a new feature? If yes, please write one phrase about this update.
• I've attached relevant screenshots (if relevant).

[vpetersson]

screenly asset set-headers 01FJVFP0QVD1E5TA70SA66AJPF "{"header1": "value1", "header2": "value2"}"

There's no reason why we need to have JSON style input. It would make more sense to set these like you would with say environment variables in Docker (e.g. -h header1=value) and then just repeat that multiple times.

[sergey-borovkov]

screenly asset set-headers 01FJVFP0QVD1E5TA70SA66AJPF "{"header1": "value1", "header2": "value2"}"

There's no reason why we need to have JSON style input. It would make more sense to set these like you would with say environment variables in Docker (e.g. -h header1=value) and then just repeat that multiple times.

Done though without short -h - it's used for help already.