Releases new fuel2 commands to operate on extensions:
fuel2 env extension enable
fuel2 env extension disable
fuel2 env extension show
fuel2 extension list
DocImpact
Also, this change introduces the option for BaseListCommand for
specifying the default fields to sort by.
Change-Id: Idee06633689efece18838766de5c4afcd24190d7
Implements: blueprint extensions-management
Partial-Bug: #1614526