Integrate gitlab-ci/add-release-suffix and 3 more

manifest_package: add release suffix

Customer specific manifest projects can now set the RELEASE_SUFFIX variable, which then gets appended to the deployment folder names.

alphaplan_fwr: change variable "release_name_local" to "release_name"

Otherwise it can be assumed that it might be correlated with outputdir_local, which is not the case.

package_release: more refactoring

Make output-dir an argument that can be passed multiple times instead of hard-coding two dirs with certain meanings.
Remove LOCALDIR variable from package.env, because it is not used anywhere (only occurence was job class ".uploadsdkftp" which wasn't used anywhere either).

package_release: refactoring

Improve readability of package_release.py and its submodule generate_release_metadata.py.

Add describing comments throughout the file.
Remove duplicate code from functions. Simplify them, so that they do what their names say (and nothing more).
Rename variables and function arguments to make their purpose clearer.
Harmonize variable names with their corresponding command line arguments.
Add pydoc for functions.
Add type declarations to function arguments.
Generate MD5 and metadata files in the source directories so that they can be copied along with the rest of the files.