recent members of "Phenom family" missing in doxygen of LALSimIMRPhenom.c

During the IMRPhenomXP(HM) review I noticed that the general "Phenom family" docs at https://lscsoft.docs.ligo.org/lalsuite/lalsimulation/group___l_a_l_sim_i_m_r_phenom__c.html have never been updated to include Pv3, Pv3HM, XPAS, XPHM (and maybe others I'm not aware of) either.

After discussing with @maria.haney we arrived at:

• The top level for the IMRPhenomX docs is https://lscsoft.docs.ligo.org/lalsuite/lalsimulation/group___l_a_l_sim_i_m_r_phenom_x__c.html ... this has been separated intentionally from the "Phenom family" docs
• However pointing to it from a single item in the list at the top of the more general family page would be helpful too ("For the IMRPhenomX family, see [link]")
• Pv3 and Pv3HM should definitely be included in https://lscsoft.docs.ligo.org/lalsuite/lalsimulation/group___l_a_l_sim_i_m_r_phenom__c.html

However, I'm only adding this here as a reminder issue at the moment, and suggest to only update the docs after !1272 (merged) has been merged, to avoid conflicts.

cc @sebastian-khan @harald.pfeiffer @sascha.husa @cecilio.garcia-quiros @geraint.pratten