Modify NSM internal GRPC connection parameters

[ljkiraly]

The following modifications needed to stabilize connections in environments where there are a lot of endpoints and nodes:

• Align the GRPC dial context timeouts in nsmgr and forwarder.

• Increase the defaut value of NSM_DIAL_TIMEOUT from 750ms to 1500ms.

• New parameter should be introduced: NSM_DIAL_MAX_DELAY which currently defaults to 120s. (https://pkg.go.dev/google.golang.org/grpc@v1.71.1/backoff#DefaultConfig)

[ljkiraly]

The default for NSM_DIAL_TIMEOUT should be bigger then backoff time (maximum value set by NSM_DIAL_MAX_DELAY).
So modified default values should be:
15 seconds for NSM_DIAL_TIMEOUT
5 seconds for NSM_DIAL_MAX_DELAY