Add missing withResponseMetadata option

[ujwaldhakal]

The withResponseMetadata option was missing from this library https://github.com/googleads/google-ads-php/blob/main/src/Google/Ads/GoogleAds/Lib/V17/UnaryGoogleAdsResponseMetadataCallable.php\#L48 because it was using gax-php.

A discussion ticket has been opened here googleads/google-ads-php#1050

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[bshaffer]

@ujwaldhakal the withResponseMetadata option is not supported in GAX, or in any GAPIC library as far as I know - it may be supported as a custom option by Google Ads. If that's the case, we'll need to figure out how to accommodate it.

[bshaffer]

See googleads/google-ads-php#1050 (comment)