Re-structuring, clean-up, fixes for first 0.2.x release

[dalito]

This groups several changes which break compatibility with linkml-project-cookiecutter into one bigger breaking PR:

• Removes all contents from the template that can be generated with linkml generators. Don't populate project directory from template but generate its contents #24
• Avoid duplication and ambiguity in what to store where (e.g. docs, examples) Conform to expectations regarding directories for docs and for test-data #13
• Changes to using docs folder for docs. The generated project now conforms to standard mkdocs-project setup. Conform to expectations regarding directories for docs and for test-data #13
• Generated schema docs into a subfolder docs/elements Conform to expectations regarding directories for docs and for test-data #13
• Moves core example data to tests/data, related to Change tests to pytest #37
• Improve and revise setup questions (vs. original linkml-project-cookiecutter) Review copier questions / stored answers #9
• Make generation of example schema optional Only optionally create an example scheme, data, tests etc. #23
• Make less often used actions optional (PyPI-release & docs preview in PRs) Make pypi & docs-preview actions optional via copier config #33
• Add "Unlicense" as another license option Add unlicense #38
• Review command names and help Review command names and help messages #34
• Remove make support Remove make and related compromises #2
• Add a copier-migration for updating to 0.2.0 to help adapting the new directory structure (c4e92c8)
• Add generation of pydantic datamodel (16f1170)
• Generate more complete Python package Created project should be a proper Python package #36

Closes #2
Closes #9
Closes #13
Closes #23
Closes #24
Closes #33
Closes #34
Closes #36
Closes #37
Closes #38