Testcontainers Java sample: fix test assertions and wait loop, modernize JDBC/JUnit, and clean up POM

[MayurMallavSaikia]

Test stability and correctness

• Add a small sleep and a timeout in the “wait until DB is available” loop to avoid busy-waiting forever on a failing setup.

• Fix assertEquals argument order (expected first, then actual) in TestRDS.

Code hygiene

• Use try-with-resources for Statement and ResultSet in RDS.test_connection to ensure they are reliably closed.

Dependency updates and cleanups (in pom.xml)

• Remove duplicate software.amazon.awssdk:s3 entry.

• Remove unused AWS SDK v1 test dependency (com.amazonaws:aws-java-sdk-s3). Project already uses AWS SDK v2.

• Update JUnit 4 to 4.13.2 (latest 4.x) to address old CVEs.

• Update PostgreSQL JDBC driver to a modern version (e.g., 42.7.4).

• Optionally update Testcontainers LocalStack module and AWS SDK v2 BOM to recent stable versions.

README

• Add direct CLI instructions to run the test without an IDE (mvn -q -Dtest=TestRDS test).

• Explicitly document prerequisites (Docker running, LocalStack Pro token) and how credentials are provided in the test.