stac-model release workflow, new stac-model-release, align release on pypi and in .toml

[rbavery]

this addresses #13 and I can test and make a release with this workflow once the PR is merged.

The release workflow is to make a release in the Github UI and tag it accordingly with stac-model-v or v in order to publish either the stac-model package or the JSON schema, respectively.

Description

• Adds a job publish-pypi to publish.yaml to publish the stac-model package to PYPI if the tag starts with stac-model-v
• adds a condition to deploy-schema (renamed from deploy) to run if tag starts with v
• updates stac-model version to match what's on PYPI: version 0.1.2

Related Issue

• fixes Invalid stac-model version on PyPI #13

Type of Change

• 📚 Examples, docs, tutorials or dependencies update;
• 🔧 Bug fix (non-breaking change which fixes an issue);
• 🥂 Improvement (non-breaking change which improves an existing feature);
• 🚀 New feature (non-breaking change which adds functionality);
• 💥 Breaking change (fix or feature that would cause existing functionality to change);
• 🔐 Security fix.

Checklist

• I've read the CONTRIBUTING.md guide;
• I've updated the code style using make codestyle;
• I've written tests for all new methods and classes that I created;
• I've written the docstring in Google format for all the methods and classes that I used.

Note: duplicate of #14, re-opened as an origin branch to check merging rules since #14 did not allow me to merge with an approving review.