Added new button to launch the new
stage form for customisable cycle
analytics.

Move add stage button to vue component

Toggle active state of the add stage button

Added customisable_cycle_analytics_form feature flag

Added basic test for add stage button

Move css to bootstrap classes

Removes scss styling that can be applied
via bootstrap classes and adds the relevant
classes to html elements

Update gitlab.pot file

Move to ee dir

Move all the add stage button
code to the relevant ee directory

Added feature tests for add stage button

Moved add stage functionality to ee mixin

Created addStageMixin for the add stage
functionality needed in EE. Added a stub
mixin to the CE dir.

Additional tests for addStageForm classes

Moved to analytics dir

Moved the add stage button
code to the relevant ee/analytics
directory where it will live