Promise support for MetadataService#request

[nwalters512]

• This is a feature with version 2.x of the SDK

Is your feature request related to a problem? Please describe.
Virtually every request supported by the SDK supports calling .promise() on the result so that it can be used without callbacks. This is described in the documentation here: https://docs.aws.amazon.com/sdk-for-javascript/v2/developer-guide/using-promises.html. However, MetadataService#request does not offer .promise() support.

Describe the solution you'd like
I'd like to be able to call MetadataService.request(...).promise().

Describe alternatives you've considered
We currently use util.promisify() to wrap request in a Promise, but that's less than ideal.

Additional context
This was originally proposed in #2062, but it was subsequently closed automatically without a resolution.

[github-actions]

Greetings! We’re closing this issue because it has been open a long time and hasn’t been updated in a while and may not be getting the attention it deserves. We encourage you to check if this is still an issue in the latest release and if you find that this is still a problem, please feel free to comment or open a new issue.

[nwalters512]

This is still an issue. The v3 SDK does not offer support for the Metadata Service: aws/aws-sdk-js-v3#4004.