Types: Register guest requires opts even though they seem to be not required

[MTRNord]

Describe the bug https://github.com/matrix-org/matrix-js-sdk/blob/develop/src/client.ts#L6900 defines opts as a mandatory arg while after that making it optional as well as having body optional.

This leads to An argument for 'opts' was not provided. with typescript.

Expected behavior opts probably should have been marked as optional?

[MTRNord]

(Also the example on the function has the await in the wrong place I think)