Add speakeasy pagination to sdk

[Flo4604]

For speakeasy to know about paginated endpoints, we need to use the x-speakeasy-pagination directive.

This is currently only used by the listIdentities endpoint, but should be used by all endpoints that we have a cursor for.

Openapi spec hast to be adjusted and the speakeasy sdk has to be generated locally against the local openapi spec in order to test this.

go/apps/api/openapi/spec/paths/v2/identities/listIdentities/index.yaml is an example of this

[linear[bot]]

ENG-2123