Where do you see the error with ISC.FeatureTracker.SSL.Config? There is nothing in the code example, that would point to using it. Why would you even use it anyway, and the error says, that this config is not enabled, you can check it here

Usually build is happening in one thread, and you would not see this error even with unlicensed version

And this error means, that you have multiple processes trying to connect to IRIS during the build

And even using Community Edition may not help, because it has a limit on connections, and you may face the same issue there too.

In some scenarios, it's possible to use multi stage building process, where you can use Community Edition image as a building stage, and target image without starting IRIS or with using only one connection, finish the build.

You can check multi-stage way with Community, or use iris.key during build stage