Add inst_checkmk to functions.sh, which resolves the release from
https://download.checkmk.com/stable_downloads.json, downloads the package
for the container's Debian release and verifies its SHA256 checksum.
CMK_VERSION now accepts:
- empty: latest stable release
- 2.4 / 2.4.0: latest patch release of a branch
- 2.4.0p18: exactly this release (no checksum available)
Package file names are taken from the JSON, so the rename from
check-mk-raw to check-mk-community in 2.5 is handled transparently.
Legacy edition names (raw, enterprise, cloud, managed) are still accepted.
CMK_BUILD is no longer needed.
checkmk now installs the latest stable release, bashclub-cmk stays on
the latest 2.4 patch release.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>