Add support for loading config from a file

[simu]

Kapitan allows users to provide additional reclass config options in a file reclass-config.yml in the inventory root directory. We add this feature to reclass-rs, but allow users to specify an arbitrary YAML file from which config options are loaded.

Additionally, we update the inventory_tests::test_render() Rust and the test_inventory() Python test cases to load the config from the already existing reclass-config.yml for the test inventory.

This PR is split out from #84

Checklist

• [x] The PR has a meaningful title. The title will be used to auto generate the changelog
• [x] PR contains a single logical change (to build a better changelog).
• [x] Update the documentation.
• [x] Update tests.
• [x] Categorize the PR by setting a good title and adding one of the labels: bug, enhancement, documentation, change, breaking, dependency, internal as they show up in the changelog
• [x] Link this PR to related PRs or issues.

[github-actions[bot]]

Benchmark for cb0c952

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| Test | Base | PR | % | |------|--------------|------------------|---| | Reclass::inventory() multi-threaded | 1609.8±108.40µs | 1612.4±134.00µs | +0.16% | | Reclass::inventory() single-threaded | 3.6±0.11ms | **3.5±0.04ms** | **-2.78%** |

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Benchmark for f58ee74

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| Test | Base | PR | % | |------|--------------|------------------|---| | Reclass::inventory() multi-threaded | 1652.3±116.28µs | 1596.8±59.52µs | -3.36% | | Reclass::inventory() single-threaded | 3.7±0.21ms | **3.6±0.09ms** | **-2.70%** |

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Benchmark for 0a35f51

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| Test | Base | PR | % | |------|--------------|------------------|---| | Reclass::inventory() multi-threaded | 1600.7±117.09µs | 1588.5±90.37µs | -0.76% | | Reclass::inventory() single-threaded | 3.6±0.09ms | 3.6±0.03ms | 0.00% |