BBH pipeline: write eccentricity params to file, add CLI to compute params & plot

[nilsvu]

Proposed changes

Creates plots of the path through orbital parameter space like this:

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Code review checklist

• The code is documented and the documentation renders correctly. Run
  make doc to generate the documentation locally into BUILD_DIR/docs/html.
  Then open index.html.
• The code follows the stylistic and code quality guidelines listed in the
  code review guide.
• The PR lists upgrade instructions and is labeled bugfix or
  new feature if appropriate.

Further comments

[nilsdeppe]

Not a review, just small question/idea :)

[nilsdeppe]

just a quick glance because I'll adapt a lot of this to BNS at some point. Should the threshold be specifiable somewhere? In SpEC we've had a harder time getting lower eccs for high q & chi runs. So much so that sometimes in BFI we just override the BFI-based target ecc.

[nilsvu]

Yes definitely, we can just make it a parameter, that's very easy to do

[knelli2]

@nilsvu I'll review after conflicts are fixed

[nilsvu]

rebased