ci: add reusable release workflow

[wpbonelli]

Implement #84 a reusable, configurable release workflow for EC Python projects. Also some test fixes.

[wpbonelli]

before proceeding maybe best to

• consider versioning approaches for EC python projects, whether it is worthwhile to adopt setuptools_scm, versioneer, or a similar tool first discussed w.r.t flopy, or continue ad-hoc versioning

• de-duplicate update_version.py (currently in flopy, mf6 and other repos) and relocate versioning utils to modflow-devtools

• discuss develop branch placeholder version string convention, is there a PEP 440-compliant way to attach a label to the previous release number i.e., not have to guess the next-released version?

  • https://github.com/modflowpy/flopy/pull/1854
  • https://github.com/modflowpy/flopy/pull/1859#issuecomment-1613988840
  • https://github.com/MODFLOW-USGS/modflow6/pull/1283