In commit 3e369bcf9, the `code` field for api/deactivate-own-user
was incorrectly documented as "BAD_REQUEST", which is the code for
the similar error returned by api/deactivate-user.
Corrects the error code to be "CANNOT_DEACTIVATE_LAST_USER" and
adds documentation for the two other fields returned by this
error response.
Note that the descriptions for the fields are added in the error
response schema will not be rendered in our current documentation.
They are rendered in other third-party tools and are therefore
good to have in our OpenAPI documentation. The description that
will be rendered in our documentation is the general error response
schema description and that is also updated for details about the
extra fields in this error response.
5774486c12