[MAINTENANCE] Add fastapi to docker-compose for mercury

[tyler-hoffman]

See title.

This should resolve tests that fail when attempting to reach 1.0 endpoints. To verify, this reverts https://github.com/great-expectations/great_expectations/pull/9946, which was a temporary workaround.

This adds nginx as a reverse proxy on port 5000. Note that we used to serve flask on port 5000, so this just scoots it out of the way to port 5001, which nginx routes traffic to.

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• [ ] Appropriate tests and docs have been updated

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