feat(config): warn unknown field instead of panic on start up

[flaneur2020]

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Summary

currently databend-query will fail loudly with any unknown field in the config file.

however, this behaviour is not very good in the sense of forward compatibiltity. sometimes we may add new config fields, but when we rollback databend-query into earlier version, it will fail for unknown field in the config file.

we can simply allow these unknown fields by simply removing the #[serde(deny_unknown_field)] attribute. however, it also has a risk that users might have typo in there config file. it's still better to have some warning about this.

this pr introduced sered_ignored while parsing the toml config file, and print a warning log for any unknown field is found.

Tests

• Unit Test

Type of change

• New Feature (non-breaking change which adds functionality)

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This change is 

[BohuTANG]

The configuration issue was caused by our actions, not the user's. Therefore, removing deny_unknown_field is not advisable, as it could negatively impact the user experience.

[zhang2014]

It is helpful for clean unused configurations.