Switch to static versioning and two-workflow release model

Replace hatch-vcs dynamic versioning with static version in _version.py
and pyproject.toml. Split CI into build.yml (test + stage draft release
on main) and release.yml (publish from draft on tag push). Docker images
are built on main pushes and re-tagged with the release version on tag
push without rebuilding.

src/ocrmypdf/_version.py

@@ -0,0 +1,3 @@
+# SPDX-FileCopyrightText: 2022 James R. Barlow
+# SPDX-License-Identifier: MPL-2.0
+__version__ = "17.2.0"