[FSSDK-10090] Refactor ODP integration

[raju-opti]

Summary

Things fixed:

• ODPManager should not be running and scheduling timer if ODP is not integrated to the project (which causes memory leak if one sdk instance is created per request)
• CreateUserContext should work even when called before the datafile is downloaded and should send the identify ODP events after datafile download completes
• Other automatic odp events (vuid registration, client initialized) should also be sent after datafile is available and should not be dropped if batching is disabled.
• ODP manager should distinguish between when odp config is still not loaded and when odp is not integrated at all
• made ODP config immutable
• ODP event manager should not schedule timers to flush events if event batching is disabled (ie batch size == 1)
• other code quality improvements

Test plan

• added new tests where applicable, and updated old tests

Issues

• FSSDK-10090

[coveralls]

coverage: 90.313% (-0.07%) from 90.381%
when pulling 117a4b5 on raju/odp_refac
into 53a2042 on master.

[mikechu-optimizely]

That was a long one phew. Thanks for putting all your thoughts in.

👇 are just some non-show stopping, thoughts/suggestions.

[muzahidul-opti]

LGTM

[mikechu-optimizely]

LGTM

[jaeopt]

One clarification - I see the updateOdpConfig on config change is broken. Can you take a look?

[jaeopt]

LGTM