Allow using Google PubSub Emulator

[lbroudoux]

Reason/Context

As of today, only WebSocket, Kafka, RabbitMQ, MQTT, and SQS/SNS are supported as asynchronous protocols because they exist as lightweight broker implementations that make sense for running in unit/integration tests.

Now that we have microcks/microcks#1846, it could be nice having the same thing for Google PubSub.

Description

The goal is to add support for Google PubSub protocol in testcontainers, allowin to configure Microcks to use a locally running Google PubSub Emulator.

Implementation ideas

This needed to be done after the release of Microcks 1.13.2 because we depend on microcks/microcks#1881

[lbroudoux]

Now done!