server: Simplify detection webhook shapes

[jailuthra]

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

Simplify detection webhook shapes - for both stream-wide configuration via auth webhook and segment-wise results via detection webhook.

Specific updates (required)

see commit history

How did you test each of these updates (required)

Updated unit test for authwebhook -> detector configuration.

Manual testing for detection results webhook:

{"manifestID":"test","seqNo":0,"sceneClassification":[{"name":"soccer","probability":0.557692289352417},{"name":"adult","probability":0}]}
{"manifestID":"test","seqNo":4,"sceneClassification":[{"name":"soccer","probability":1},{"name":"adult","probability":0}]}
{"manifestID":"test","seqNo":8,"sceneClassification":[{"name":"soccer","probability":1},{"name":"adult","probability":0}]}
{"manifestID":"test","seqNo":12,"sceneClassification":[{"name":"soccer","probability":1},{"name":"adult","probability":0}]}
{"manifestID":"test","seqNo":16,"sceneClassification":[{"name":"soccer","probability":0.9193333387374878},{"name":"adult","probability":0}]}

Does this pull request close any open issues?

Fixes #1917

Depends upon
Some changes in LPMS livepeer/lpms@b196bda which are currently a part of a working branch (jai/adddnn).
But we can ignore the dependency for now, as the target for this PR is also a working branch (jai/e2e-detection)

Checklist:

• Read the contribution guide
• make runs successfully
• All tests in ./test.sh pass
• README and other documentation updated
• Pending changelog updated

[yondonfu]

LGTM after squashing