begin can't do Unregister requests without Register requests

[NikitaSkrynnik]

Current Behavior

We can see this bug when we scale registry-k8s, for example. If one of the registries receives an Unregister request from an endpoint but this registry didn't receive Register request from the same endpoint previously, the registry just skips the Unregister request. This happens because the registry can't find an eventFactory for this endpoint. Here is the code where it happens: Code.

The situation is the same with Close request if we scale nsmgr for example. Code

Expected Behavior

The registry should delete the endpoint from etcd even if it couldn't find an eventFactory for this endpoint.

Steps to Reproduce

The steps can be found in this issue: networkservicemesh/sdk-k8s#456

[NikitaSkrynnik]

Performance comparison between recursive version of begin and channel version of begin:

goos: linux
goarch: amd64
cpu: 12th Gen Intel(R) Core(TM) i7-12700KF
                                        │ beginchannels  │              beginrecursive              │
                                        │     sec/op     │     sec/op      vs base                  │
Begin_RegisterSameIDs-20                  0.006271n ± 4%   0.004997n ± 2%   -20.31% (n=500)
Begin_UnregisterSameIDs-20                0.004392n ± 4%   0.005649n ± 2%   +28.63% (p=0.000 n=500)
Begin_RegisterUnregisterSameIDs-20        0.008200n ± 2%   0.010225n ± 2%   +24.70% (p=0.000 n=500)
Begin_RegisterDifferentIDs-20             0.003916n ± 4%   0.006073n ± 2%   +55.08% (p=0.000 n=500)
Begin_UnregisterDifferentIDs-20           0.003423n ± 4%   0.005814n ± 2%   +69.81% (p=0.000 n=500)
Begin_RegisterUnregisterDifferentIDs-20   0.006937n ± 6%   0.019170n ± 4%  +176.34% (p=0.000 n=500)
geomean                                   0.005253n        0.007617n        +45.02%