Make base URL of conda-store server a setting in the settingRegistry

[peytondmurray]

Summary

This PR makes the base URL of the conda-store server a setting in the SettingRegistry, allowing the user to change it at will. This is useful for cases where the conda-store server isn't running locally, or for example when it is configured to run on a different port than the usual http://localhost:5000.

Changes

• Add condaStoreUrl to the Conda settings in the settingRegistry; default URL is http://localhost:5000, which is what conda-store-server currently defaults to
• Instantiate the condaStoreEnvironmentManager with settings from the settingRegistry
• Pass the conda-store server URL to each of the endpoints inside the condaStoreEnvironmentManager so that they know which endpoint to fetch from

See https://github.com/Quansight/conda-store/issues/146 for more information.

[github-actions[bot]]

:point_left: Launch a binder notebook on the branch Quansight/gator/set-conda-store-url