v1.2.0 release candidate

[haykh]

Systemic Changes:

• [ ] Add a list of explicitly supported (constantly upgraded) problem generators (#92)

New Features:

• [ ] #83
• [ ] #48
• [x] #67
• [x] #70
• [x] alternative MPI communications for particles #77
• [x] field-downsampling in the output #73
• [x] writing into separate files #75
• [x] powerlaw injector #71
• [x] Two-temperature Maxwellian (being tested in #92)
• [x] Option to disable GPU-aware-MPI (#105)
• [ ] Custom injector (being tested in #92)
• [x] ~Particle purge routine (being developed in #92)~ (documented, not necessary to archetype)
• [ ] Box-reduced stats output (#106)

Improvements:

• [x] New zig-zag pusher with no explicit coordinate conversion (#98)
• [x] more consistent and general boundary condition setters (worked in #72)
• [x] check for dx=dy=dz in Minkowski now with accuracy (fixed with https://github.com/entity-toolkit/entity/pull/69/commits/5cf30afae826430c04a827e5831308bbf08cf28e)
• [x] Log level controlled from input (https://github.com/entity-toolkit/entity/pull/69/commits/ec7ff77c6cb3b1fd93701047acd67fbca9425048)

Major bugs:

• [x] #62
• [x] ~#60~ (moved to v1.1.1)
• [x] potential bug in field boundaries #72
• [x] no need for explicit HDF5_ROOT in cmake #82 (solved in #90)
• [x] #74 (fixed in #89)

Minor bugs:

• [x] warning for template declaration #81

Potentially breaking changes

• particle payloads are now a normal 2D Kokkos::View indexed as (prtl index, payload index)