dont evaluate random embeddings twice

[hahahannes]

Hi :)

I run into a small performance problem where I have multiple embeddings with the same dimensionality.
First, I created random embeddings for each of them, but this lead to quite some amount of training runs.
Then I wanted to activate random embeddings for only one of them but got an error that random embeddings are missing for the other when I run the experiment.

This is caused by https://github.com/DS3Lab/cognival-cli/blob/master/cognival/lib_nubia/commands/process.py#L575.
I see the reason behind the warning but it might be also nice to instead set a None random embedding in the config, to decrease the training time. For me this decreased the number of jobs from ~6000 to ~1800.