Adapt docker-compose-gpu.yml to use DPR by default

[ZanSara]

Changes:

• Now both docker-compose files use Julian's countries dataset
• The GPU version uses DPR as the default pipeline in the REST API
• The GPU version has the file upload disabled to be ready to deploy as the hosted version (is this OK?)

Note: This assumes that the dataset used already has embeddings for the documents it contains. So do not merge before Julian confirms that the ES image has the embeddings too.

[julian-risch]

Looks good to me! 👍