Nightly example releases

[wpbonelli]

Consider doing an MF6 examples nightly build, or include them in the MF6 nightly build. Currently we have a development version of the RTD site but we only "release" examples (i.e. build and distribute input files from the Python/FloPy scripts) at "official" MF6 release time.

The ultimate aim here is consistent versioning for MF6 and MF6 example models. Since they must be synchronized to the same set of DFNs, IMO they should be on an identical release cycle. (Moving them into the same repository is one way, but might be tricky and they have lived separate for a long time, so I am ignoring that possibility for now.)

My immediate motivation is that we already have tooling which can identify/install both official and nightly MF6 binaries (latter identified by date), but we have had no easy way of installing examples, and in any case we currently only distribute "official" examples releases. The example models API under development is a tentative solution, but ideally it should have the same version semantics as flopy's get-modflow.

Other low-hanging fruit which might dovetail with this, trading some niceties for reduced maintenance burden

• consolidate the "full" and "minimal" build flavors and make the nightly build contents identical to the official
• configure the build automation to build the examples release itself, instead of downloading the last one from the examples repo