Add more info to validation errors

[gadomski]

Related Issue(s):

• Closes Propagate error message from jsonschema to STACValidationError #901

Description:

Before, when validating an item that has a collection field but no link with rel="collection":

pystac.errors.STACValidationError: Validation failed for Feature with ID test-item against schema at https://schemas.stacspec.org/v1.0.0/item-spec/json-schema/item.json

After:

pystac.errors.STACValidationError: Validation failed for Feature with ID test-item against schema at https://schemas.stacspec.org/v1.0.0/item-spec/json-schema/item.json
"can't have a collection" should not be valid under {}

Failed validating 'not' in schema['allOf'][0]['allOf'][2]['else']['properties']['collection']:
    {'not': {}}

On instance['collection']:
    "can't have a collection"

PR Checklist:

• pre-commit hooks pass locally
• Tests pass (run scripts/test)
• Documentation has been updated to reflect changes, if applicable
• This PR maintains or improves overall codebase code coverage.
• Changes are added to the CHANGELOG. See the docs for information about adding to the changelog.

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Files	Coverage Δ
pystac/validation/stac_validator.py	78.00% <50.00%> (-0.58%)	⬇️

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[jsignell]

Nice!!