Add a witchcraft builder and make runtime configurable

[sfackler]

Before this PR

Endpoints would always use the default ConjureRuntime.

After this PR

==COMMIT_MSG==
Added the ability to configure the ConjureRuntime used by endpoints.
==COMMIT_MSG==

Like WC-Java, this is implemented via a builder API before the standard server initialization process.

This does not affect the runtime used for the status endpoints to ensure they continue to work properly.

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Description

Added the ability to configure the ConjureRuntime used by endpoints.

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✨ Features

• Added the ability to configure the ConjureRuntime used by endpoints. (#274)

[sfackler]

Here's an example of customizing the runtime using the server main macro:

#[witchcraft_server::main(conjure_runtime = Arc::new(ConjureRuntime::builder().encoding(JsonEncoding).build()))]
fn main(
    _install: InstallConfig,
    _runtime: Refreshable<RuntimeConfig, Error>,
    wc: &mut Witchcraft,
) -> Result<(), Error> {
    wc.blocking_api(TestServiceEndpoints::new(TestResource));

    Ok(())
}