Adds leads from a `leads` array of `{ profileUrl, ... }` objects (or `{ email, ... }` when the workspace has the email channel, see `LeadInput`), or imports a whole lead list with `listId`. The workspace lead is upserted from the fields you pass and enrolled in one call — you don't need to create leads separately first. Caller-supplied fields win over the best-effort LinkedIn lookup. Leads already in the campaign are skipped. Max 1000 leads per request. Every enrolled lead is also saved to the campaign's own list, created on the first enrollment and named "<campaign name>'s leads" (exposed as `listId` on the campaign). That list and the campaign stay in step: adding leads to it enrolls them, removing leads from it removes them from the campaign. Leads imported with `listId` keep their source list too. The response's `listId` is the campaign's own list for a `leads` array, or the source list for a `listId` import.