Run the Annex A data tests against a released MobilityDB

[estebanzimanyi]

The abstract tests that read or write data skip without a database, so continuous integration exercises the routing table and the document assembly and not the lifecycles. A service container gives them one, and the same ats_live_test.go that skips by name offline runs there.

The image is a released MobilityDB rather than master. A conformance claim names a version somebody can install, and one resting on an unreleased branch names nothing a reader can obtain. The eight groups the job covers against mobilitydb/mobilitydb:18-3.6-1.3 are the collections and collection documents, the features and one feature, the temporal geometry with its distance and velocity queries and its 501 acceleration answer, the temporal properties of all four stored types, both write lifecycles, and the closing read-back of the fixture.

A skip is not a pass. MFAPI_DSN is what makes these tests run at all, and a job that lost it would exercise nothing while still reporting success — the failure this job exists to prevent. The run therefore requires no skip and at least one pass, and fails otherwise.

The job triggers on pull_request, so this pull request exercises it rather than leaving it unproven until a later trigger.

Future: with a database in the job, the schema validation can be pointed at real documents rather than scripted ones. That waits on the MF-JSON datetime offset, which openapi/README.md records — a temporal geometry's datetimes carry no format in the schema, so validating them needs the encoder to write the offset minutes RFC 3339 requires.