feat: add setHeader conditional value types

[xseman]

Improve setHeader type hinting for standard headers based on @types/node.

e.g.

// `name: "authorization"` hints👇
setHeader(name: "authorization", value?: string | undefined): void

// `name: "accept-charset"` hints👇
setHeader(name: "accept-charset", value?: string | string[] | undefined): void

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• [x] Have you checked to ensure there aren't other open Pull Requests for the same update/change?

[WoH]

Thanks!