feat(compute/metadata): add http timeout to metadata client

[therealmitchconnors]

Fixes #6498

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[therealmitchconnors]

I think this is a reasonable request but that is a rather short timeout. Could be make this 5 seconds at least to start. We have similar timeouts elsewhere in this package.

I have updated to 5 seconds. Please note that the dial timeout is still set to 2 seconds, so the timeout behavior will vary depending on the specifics.