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?

  • fix(version): comply with pep 440 for dev version str modflowpy/flopy#1854
  • Post release 3.4.1 reset modflowpy/flopy#1859 (comment)
  • ci(release): reinit release notes, update dist scripts modflow6#1283