Fix pattern-matched init_config when using a single-module formulation

[PhilMiller]

Spurred by testing added to cover the changes in #906

Additions

• Test using {{id}} in the init_config property of a single-module formulation, configured either globally or for the specific catchment

Changes

• Use configuration with {{id}} substituted for the catchment's ID in call paths for global and catchment-specific formulations

Checklist

• PR has an informative and human-readable title
• Changes are limited to a single goal (no scope creep)
• Code can be automatically merged (no conflicts)
• Code follows project standards (link if applicable)
• Passes all existing automated tests
• Any change in functionality is tested
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged / future todos are captured in comments
• Project documentation has been updated (including the "Unreleased" section of the CHANGELOG)
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[robertbartel]

This looks good. I may come back to it in the future to add tests that more directly test things, and/or push for a larger overhaul of the configuration management code. If you have any thoughts on the latter @PhilMiller, especially in the near term, let me know. But this addresses things well for now.