REST API: Add new query attribute "draft" for merge requests instead of "wip"
## Issue As stated in [the documentation](https://docs.gitlab.com/api/merge_requests), there is a `wip` query attribute that allows to return only no/draft merge requests. However, the response includes a `work_in_progress` attribute, which has been deprecated in favor of the new `draft` attribute. These are all different, inconsistent names: * `wip` * `work_in_progress` * `draft` Another inconsistency is that the `wip` query attribute is the only one that uses `yes`/`no` instead of `true`/`false`, making it difficult to use. ## Proposal Add a new `draft` query attribute with `true`/`false` values ​​that replicates the behavior of `wip`. Deprecate the `wip` query attribute. Thus, both request and response attributes will be called `draft`, and all boolean attributes will use values ​​of `true`/`false`.
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