Review API endpoint responses inconsistencies

[GGP1]

Branch	Component
20748-upgrade-to-connexion-3	RESTful API

Description

During #22478, we have found some inconsistencies in the responses of some endpoints. These were

• GET /cluster/healthcheck uses "n/a" for unknown fields instead of "N/A" in uppercase like the rest. The information comes like this from the database, but to be consistent we should modify it to be consistent with the other responses.

• The response of the endpoint GET /syscollector/:agent_id/packages has two fields location and install_time that are equal to " " on most items. The same happens in GET /syscollector/:agent_id/ports with process.

  This is because the database contains an empty space, we should consult with the core team to see if this is the desired behavior.

Checks

The following elements have been updated or reviewed (should also be checked if no modification is required):

• Tests (unit tests, API integration tests).
• Changelog.
• Documentation.
• Integration test mapping (using api/test/integration/mapping/_test_mapping.py).