Add EP angle to McCollisions for debugging

[ddobrigk]

This PR adds the event plane (reaction plane -> the angle of inclination of the impact parameter from PYTHIA) to the McCollisions table. It is necessary as a development for the v2 MC closure testing. Note that, if the data model change is accepted, a converter will be written and committed to O2Physics before the McCollisions table version is actually bumped to 001.

The current size of the McCollisions table in our Pb-Pb MC is 0.002% of all compressed space, and it is comprised of 6 floats and one short. Adding one float to it will result in negligible disk space use that is well worth the cost. I would be happy to present the case for this in one of the WP4+WP14 meetings, of course. Thank you!

Tagging @sawenzel @pzhristov @ktf