fix(client): provide an option to fix an issue where the target service cannot be found when a client using generic calls a multi-service server

[Marina-Sakai]

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[felix021]

As suggested by Emma, it's better (easy to use and understand) to retrieve the Service Name from the generic call form:

gCli.Call(ctx, "$svc/$method", ...)

And since it's a derived option, even if it's not added to Kitex, users can achieve the goal without it.

Therefore I think currently we better not merge.