Previously, new cops were introduced as either enabled or disabled. The
ones enabled were bothering users with new offences, while disabled cops
were often left out and remained under radars, while still being useful.

By introducing this special status, users have to decide how to handle
new cops, by explicitly enabling or disabling them.

Cops are to be introduced with pending status between major releases of
RuboCop and its extensions, and they eventually become enabled or
disabled on major releases.

Co-authored-by: Phil Pirozhkov <hello@fili.pp.ru>