Move build log feature extraction to outside of Pulse

Currently we use Pulse's regex-based postprocessor to extract valuable error messages from build logs.

We have >100 regexes built up "organically" over the course of some years.
Currently this information lives purely in the Pulse configs and nowhere else.

These should be extracted into a separate script, with the benefits that:

• we can write tests for the analysis script (i.e. "here's a build log, I expect that you extract this text")
• proper revision control for the patterns
• we can document the meaning of the patterns (seems impossible in Pulse)
• script can be used outside of Pulse on any plain text files