Provide PREFECT_SERVER_VERSION to Apollo image CI build step

[joshmeek]

Currently when running the Apollo container you will see the output:

apollo_1    | Server ready at http://0.0.0.0:4200 🚀 (version: UNKNOWN)

This is due to the PREFECT_SERVER_VERSION not being provided to the Docker image build:

https://github.com/PrefectHQ/server/blob/bddc98bd7c29eb7d1cad89c9206165e6c8d8f134/.circleci/config.yml#L211-L223

https://github.com/PrefectHQ/server/blob/bddc98bd7c29eb7d1cad89c9206165e6c8d8f134/services/apollo/Dockerfile#L3