Sorna-manager

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- Improve packaging: auto-converted README.md as long description and unified
requirements.txt and setup.py dependencies.

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- Fix internal API mismatch bug in web termainl.

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- Fix sorna-common requirement version.

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**IMPROVEMENTS**

- Handle v1/v2 API requests separately.
Now it preserves old "aggregated" stdout/stderr/media outputs for v1
but uses the new streaming outputs for v2.
(v1 API users can use streaming as well, but they will loose the
ordering information of individual lines of the console output.)

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**FIXES**

- Fix task pending error during shutdown due to missing await for redis
monitoring task after cancelled.

- Fix wrong active instance count in Datadog stats due to missing checks for
shadow in InstanceRegistry.enumerate_instances()

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**FIXES**

- Prevent potential CPU-hogging infinite loop during Datadog stats updates.

**IMPROVEMENTS**

- Add statistics reporting via Datadog. (optional feature)

- Improve exception handling and reporting, particularly for agent-sid errors.