Support additional plugin function parameters

[trivikr]

Issue #, if available:
Refs: aws/aws-sdk-js-v3#2211
Similar to: #302

Description of changes:
Currently the generated command calls additional runtime plugins, but
it only takes 1 parameter. To support endpoint discovery, we have to
pass more parameters which are specific to commands as follows:

    this.middlewareStack.use(
      getEndpointDiscoveryOptionalPlugin(configuration, {
        clientStack,
        options,
      })
    );

In the above example, the clientStack and options passed to the plugin
are used for calling endpoint discovery command.

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[AllanZhengYP]

cc @kstich for a look