Expand tildes when resolving Ruff server configuration file

[charliermarsh]

Summary

Users can now include tildes and environment variables in the provided path, just like with --config.

Closes #11277.

Test Plan

Set the configuration path to "ruff.configuration": "~/x.toml"; verified that the server attempted to read from /Users/crmarsh/x.toml.

[github-actions]

ruff-ecosystem results

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