Fixes after tests

[EricaCandido]

See #188.

This PR:

• jsonld create now runs when data.yaml* is absent — the step condition previously only checked needs_jsonld; it now also triggers when data_exists == 'false', so assets without any data file are correctly processed.
• Avoids duplicate data file generation when data.yaml* already exists. The step now reads the existing filename from check-files outputs and uses it as the output target, preserving the original extension.

Example

Before the fix:

Asset has subject-disciplines.data.yamlld, the step runs with:

--output subject-disciplines.data.yaml   ← new file, different extension

Result: both subject-disciplines.data.yamlld and subject-disciplines.data.yaml exist.

---

After the fix:

check-files finds subject-disciplines.data.yamlld → data_file=subject-disciplines.data.yamlld

The step runs with:

EXISTING_DATA="subject-disciplines.data.yamlld"
OUTPUT_FILE="subject-disciplines.data.yamlld"   ← same file, overwritten in place
--output subject-disciplines.data.yamlld

Result: only subject-disciplines.data.yamlld exists, updated in place.

• Generated data file is listed in the auto-PR body — the jsonld create step now exports data_file as an output; the PR body includes it conditionally alongside the .db artifact.

• Also supports .data.yamlld as input for apistore create — the --jsonld argument was hardcoded to ${ASSET_NAME}.data.yaml; it now reads the filename from check-files outputs, which matches both .data.yaml and .data.yamlld.

• apistore create was receiving an empty --jsonld argument when jsonld create had just generated the data file in the same run — check-files runs before jsonld create, so data_file was empty at that point. The step now prefers jsonld-create outputs and falls back to check-files outputs when the file already existed.

• jsonld create now runs when data.yaml* is absent — the step condition previously only checked needs_jsonld; it now also triggers when data_exists == 'false', so assets without any data file are correctly processed.