Write one topic category per value from comma-separated strings

[epifanio]

Problem

Repositories store several ISO topic categories as one comma-separated string (topicategory is a Text column), and two places mishandle that:

1. OGC API - Records / STAC (record2json): a list becomes one theme concept per entry, but a string becomes one concept holding the whole string:

   {"concepts": [{"id": "climatologyMeteorologyAtmosphere,environment"}], "scheme": "…#MD_TopicCategoryCode"}

   Other keyword themes on the same record get one concept per keyword.
2. apiso / iso19115p3 profiles: the loop over val.split(',') writes val instead of v, so a record with two categories gets two gmd:topicCategory (or mri:topicCategory) elements, both containing a,b.

Change

• record2json: split a string topicategory on commas into one concept per (stripped, non-empty) value. Lists are handled as before.
• apiso / iso19115p3: write the current value v.strip() in each MD_TopicCategoryCode.

Tests

• New tests/unittests/test_ogc_api_records.py: a single value, two comma-separated values, extra spaces and a trailing comma, and a list. The two comma-separated cases fail without this change.
• Unit: 163 passed. Functional (not harvesting and not distributedsearch and not pubsub): 410 passed. No functional test record has several topic categories, so no expected output changes.
• Seen in production on a record with climatologyMeteorologyAtmosphere and environment, whose Records API theme was the single concept climatologyMeteorologyAtmosphere,environment.