api: New API to get playback URL from an identifier

[victorges]

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

This creates an API to facilitate and create a consistent interface for creating a playback URL
given an identifier. It could be either a stream or asset playback ID, or also a recorded session
ID and it will return a response in the same format containing the corresponding HLS playback URL.

The context for this is the creation of the Lens publication video NFTs with an embeddable HLS player.
Ideally the NFT would have no internal identifiers from livepeer.com, maybe referencing assets by their
CIDs instead. While we don't do that, we can at least simplify that internal identifier and only provide a
playback ID (additionally from the CID of the original file). The playback ID will be used to playback
a pre-processed version of the video in an optimized format.

Having this API also makes these NFTs future-proof, since we will be able to change their format without
it breaking every previously minted NFT that had the broken references. The reference will be only a simple
playback ID and we can change the response of that API freely.

This also has a soft dependency on #1051 but they can be deployed independently. It's also based on top of
#1014 but I believe it can also be rebased, no strict dependencies in the code.

Specific updates (required)

• Create new API for resolving the playback URL
• Add tests 🙌

-

• How did you test each of these updates (required)
  yarn test ✨

Does this pull request close any open issues?

Implements #1058

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.

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Name	Status	Preview	Updated
livepeer-com	✅ Ready (Inspect)	Visit Preview	May 26, 2022 at 11:49PM (UTC)

[codecov]

Codecov Report

Merging #1075 (bf54844) into master (ee0c219) will increase coverage by 3.92880%.
The diff coverage is 69.33333%.

❗ Current head bf54844 differs from pull request most recent head c417d6b. Consider uploading reports for the commit c417d6b to get more accurate results

@@                 Coverage Diff                 @@
##              master       #1075         +/-   ##
===================================================
+ Coverage   45.68115%   49.60995%   +3.92879%     
===================================================
  Files             64          66          +2     
  Lines           4052        4102         +50     
  Branches         708         690         -18     
===================================================
+ Hits            1851        2035        +184     
+ Misses          1987        1839        -148     
- Partials         214         228         +14     

Impacted Files	Coverage Δ
packages/api/src/app-router.ts	54.05405% <ø> (ø)
packages/api/src/webhooks/cannon.ts	48.25581% <0.00000%> (-0.28221%)	⬇️
packages/api/src/controllers/session.ts	15.83333% <20.00000%> (+9.72645%)	⬆️
packages/api/src/task/scheduler.ts	41.53846% <28.57143%> (+35.98290%)	⬆️
packages/api/src/controllers/asset.ts	37.82609% <67.85714%> (+30.50901%)	⬆️
packages/api/src/controllers/playback.ts	90.32258% <90.32258%> (ø)
packages/api/src/controllers/stream.ts	48.89937% <100.00000%> (+0.62892%)	⬆️
packages/api/src/index.ts	49.09091% <100.00000%> (ø)
packages/api/src/store/asset-table.ts	100.00000% <100.00000%> (ø)
packages/api/src/store/db.ts	82.02247% <100.00000%> (ø)
... and 13 more

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[hjpotter92]

lgtm