Provide option for proxy_wasm::createWasm() to bypass canary

[mpwarres]

Currently, proxy_wasm::createWasm() always canaries the provided plugin. This provides assurance that the given plugin will be able to start successfully in the returned WasmBase instance.

However in some use cases, particularly ones that do not involve sharing or reuse of the WasmBase, it may be desirable to skip the canary step, to avoid doubled calls to WasmBase::start() and WasmBase::configure().