www/asset: Fix "processing" progress update

[victorges]

What does this pull request do? Explain your changes. (required)

This introduces a little delay after finishing upload so that there's time for the
task to start executing. This will guarantee that we will show a swift update from
"uploading 100%" to "processing x%" instead of taking up to 10 seconds depending
on the refresh interval.

Specific updates (required)
Create a sleep helper and use it to delay state invalidation.

-

• How did you test each of these updates (required)
  Upload on the vercel preview and check described behavior.

Does this pull request close any open issues?
No only my "OCD".

Checklist:

• I have read the CONTRIBUTING document.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.

[vercel]

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Name	Status	Preview	Updated
livepeer-studio	✅ Ready (Inspect)	Visit Preview	Nov 13, 2022 at 8:38PM (UTC)

[codecov]

Codecov Report

Merging #1458 (4402765) into master (afb5d9c) will not change coverage.
The diff coverage is 0.00000%.

@@              Coverage Diff              @@
##              master       #1458   +/-   ##
=============================================
  Coverage   53.00000%   53.00000%           
=============================================
  Files             68          68           
  Lines           4500        4500           
  Branches         846         846           
=============================================
  Hits            2385        2385           
  Misses          1809        1809           
  Partials         306         306           

Impacted Files	Coverage Δ
packages/api/src/controllers/asset.ts	59.34426% <0.00000%> (ø)

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Impacted Files	Coverage Δ
packages/api/src/controllers/asset.ts	59.34426% <0.00000%> (ø)

[0xcadams]

LGTM