Add `--version` flag

[cmungall]

As per https://clig.dev/ we should have a --version flag on generator and other commands. This should display the linkml version - perhaps also runtime.

not sure how to implement this:

>>> import linkml
RDFLib Version: 5.0.0
>>> linkml.__version__
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: module 'linkml' has no attribute '__version__'

[rosdyana]

@cmungall I think we can use versionner (https://github.com/python-versioneer/python-versioneer/blob/master/INSTALL.md).

[cmungall]

We need to solve this problem generally:

• the metamodel docs should show the version of linkml-model
• generated schemas should show the version of the schema in their own docs
• all tools should be able to report on the version of that tool, and also the version of the metamodel

The general blocker here is that we use github releases to handle all aspects of releases, including assigning version tags. This means the versions in all out pyproject.yaml files is 0.0.0, making introspection hard.

[dalito]

For automatic versioning with poetry, you may use https://github.com/mtkennerly/poetry-dynamic-versioning - It solved poetry`s automatic versioning problem for me. The version can be derived from a git-tag and temporarily injected to files you want. Can this not solve the 0.0.0 problem? You inject into the released files but not into the versioned code.

[cmungall]

oooh this may be just what we need!! thank you @dalito!