refactor: `fastFailMetadataRequest` to use `Promise.any`

[danielbankhead]

We can streamline fastFailMetadataRequest by using Promise.any in Node 15+ rather than Promise.race:

https://github.com/googleapis/gcp-metadata/blob/92f258ca6a62160ed9b9bdedf15a2ae147f4f35c/src/index.ts#L179-L229

[Dhoni77]

Hi @danielbankhead I would like to work on this

[danielbankhead]

Thanks @Dhoni77; note that this will require us to Node 16 (next stable), which will not happen for some time.