Upgrade Testcontainers from 1.20.1 to 2.0.5

[porunov]

Testcontainers 1.x bundles a docker-java client that defaults to Docker Engine API version 1.32. Docker Engine 29 raised its minimum supported API version to 1.40 and rejects older clients, so every Testcontainers-based test fails to find a valid Docker environment ("client version 1.32 is too old"). Pinning the API version on 1.x is insufficient because 1.x's environment detection itself fails against Docker 29. Testcontainers 2.0.x negotiates a compatible API version and restores compatibility with current Docker.

Testcontainers 2.0 renamed its Maven modules with a testcontainers- prefix (e.g. org.testcontainers:cassandra -> org.testcontainers:testcontainers-cassandra), so the dependency artifactIds are updated accordingly. The Java packages are unchanged in 2.0, so no test source changes are required. Testcontainers 2.0.0+ is compiled for Java 8 bytecode and therefore remains compatible with JanusGraph's build.

Verified locally against Docker Engine 29 that the CQL, HBase, Elasticsearch and Solr Testcontainers tests start their containers and pass.

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