Fix some interpolation of config in Prefect server dev commands

[lauralorenz]

• Convert ui_path when read from environment variable into a Path object.
• Use config file's host and port for hasura and apollo when starting services with dev services.

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What does this PR change?

Fixes some config interpolation that wasn't happening when running services independently/not with docker.

Why is this PR important?

Needed to dev on Apollo from Prefect Core; Apollo services could not build Apollo schema or healthcheck Apollo when running from dev services without it. Also needed to be able to build the UI from the env variable path instead of the default.

[jlowin]

@lauralorenz makes total sense for dev work but I think these env vars set the docker-compose environment as well, and I think that localhost won't properly be recognized inside the docker compose environment; it'll need to resolve the service name ("hasura", "graphql", etc.)

Potentially, since we know the docker-compose file with certainty, we should just not all the hostname to be specified and use hardcode the service names instead in docker-compose.yaml

[lauralorenz]

@jlowin

I have that the prefect server start command aka the docker compose based setup is controlled by config set in this file: https://github.com/PrefectHQ/prefect/blob/master/src/prefect/cli/server.py#L26-L39

and that the changes in this PR are to a different file, which is only used by the prefect-server dev services and prefect-server infrastructure commands.

[jlowin]

Ah, I apologize, I didn't realize it was two different files! 👍

[cicdw]

To avoid the reasonable confusion that @jlowin had I think we should rename the server/cli/dev make_env function to make_dev_env to clarify that it is purely for development purposes. (and it's associated calls)

[codecov]

Codecov Report

Merging #2299 into master will increase coverage by 0.01%.
The diff coverage is n/a.