Add MongoDB init script regression test

[HuseynBlv]

Summary

Related to #3066.

This PR adds a regression test for MongoDB init script support in MongoDBContainer.

The new test verifies that a JavaScript init file copied into /docker-entrypoint-initdb.d/mongo-init.js is executed during MongoDB startup, and that the data inserted by the script is available after the container starts.

Context

MongoDB Docker images support initialization scripts placed under /docker-entrypoint-initdb.d/. This is useful in tests where users want to create initial databases, collections, users, or seed data automatically when the container starts.

This PR adds test coverage for that behavior in MongoDBContainer, so future changes do not accidentally break init-script support.

Changes

• Added shouldRunInitScript() to MongoDBContainerTest
• Added a small mongo-init.js test resource
• The test:
  • copies mongo-init.js into /docker-entrypoint-initdb.d/mongo-init.js
  • starts MongoDBContainer
  • connects to MongoDB after startup
  • verifies that the init script inserted the expected document
• No production code changes
• No dependency changes
• No new module added

Verification

Ran:

./gradlew checkstyleMain checkstyleTest spotlessApply

./gradlew spotlessCheck

./gradlew :testcontainers-mongodb:test --tests "org.testcontainers.mongodb.MongoDBContainerTest.shouldRunInitScript"