Declare nmdc-schema as a Python dependency

[pkalita-lbl]

This is related to #258. Part of that task will be generating a new enum in submission-schema based on an enum in nmdc-schema plus some business logic. These changes will make it easier to accomplish that. Plus, they address the large number of places the nmdc-schema version number needs to be changed when upgrading currently.

The main idea here is to declare nmdc-schema as a normal Python dependency in the dev Poetry group. All build steps that require nmdc-schema as a YAML file on disk now use local/nmdc.yaml. This file in turn is extracted from the Python package by a small script instead of being fetched from GitHub.

Updating the version of nmdc-schema used by the build process is now a matter of doing a normal Python dependency update, as noted in the README.

[eecavanna]

Looks good to me! I left one comment, which was about adding a description to the click command's help text.

[pkalita-lbl]

I locally resolved the merge conflicts. However once they were resolved the project's virtual environment became uninstallable:

Because nmdc-schema (11.3.0) depends on mkdocs-mermaid2-plugin (>=0.6.0,<0.7.0)
 and nmdc-submission-schema depends on mkdocs-mermaid2-plugin (^1.1.0), nmdc-schema is forbidden.
So, because nmdc-submission-schema depends on nmdc-schema (11.3.0), version solving failed.

This project's mkdocs-mermaid2-plugin dependency got updated recently in #296. And that's fine. But there is no need for nmdc-schema to list mkdocs-mermaid2-plugin as a non-dev dependency. See: microbiomedata/nmdc-schema#2328

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[turbomam]

This looks good for your needs as well as just being easier to maintain. Thanks.