feat: add meta_type config

[lichuang]

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Summary

feat: add meta_type config

meta_type has these types: remote, Fallback and embedded, use Fallback as default.
Fallback is used for forward compatbility, that is:
First check embedded config, then endpoints, finally address.

Fixes #8455

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1 Ignored Deployment

Name	Status	Preview	Updated
databend	⬜️ Ignored (Inspect)		Nov 3, 2022 at 6:34AM (UTC)

[drmingdrmer]

It's able to serialize an enum directly(looks good in our case?):

#[derive(serde::Serialize, serde::Deserialize)]
enum Foo {
    #[serde(rename = "a")]
    A,
    #[serde(rename = "b")]
    B,
}

    let a = Foo::A;
    let s = serde_json::to_string(&a).unwrap();
    println!("{}", s); // "a"