Peak processing plugin has insufficient condition for TF2 checking

Created by: decibelcooper

Hello,

In attempting to walk through beginning tutorial steps, I came across a tensorflow failure to find graph elements at straxen/plugins/peak_processing.py", line 222. E.g.,

ValueError: Tensor Tensor("dense_6/BiasAdd:0", shape=(?, 2), dtype=float32) is not an element of this graph.

Upon investigation, I see that special cases were put into place for the peak_processing plugin to use tensorflow v2. Unfortunately, it looks like the condition for checking for v2 is insufficient. https://github.com/XENONnT/straxen/blob/62d964d277729e48d5648d04669ed7fa927b8d62/straxen/plugins/peak_processing.py#L176

Perhaps one could use parse_version(tf.__version__) >= parse_version('2.0.'), since 2.0 is still pre-release?