For the variables list in CI/CD settings
this commits adds an header row with titles

- rewords examples starting with 'should'
- rewords examples starting with 'it'

Note: I had to manually fixup "onlies" to "only"

Simple masking frontend - CE

See merge request gitlab-org/gitlab-ce!26751

Show masked switch for each variable
When toggled on, the variable value will be masked in runner logs
Show warning message if the switch is on but the value is not maskable

* Extend quick actions dsl to allow specifying model types
to which given quick action applies
* Rename issuable attribute to noteable in interpret_service.rb
* Refactor and reorder quick action specs
* Create a shared example spec for each quick action to be used for
issue, merge request and commit specs.

https://gitlab.com/gitlab-org/gitlab-ce/issues/50199

This reverts merge request !25476

Add a masked switch to variable rows
Copy some behavior from the protected switch

Updated nav-sidebar to reflect the documented
behaviour from the design.gitlab.com docs:
https://design.gitlab.com/regions/navigation#contextual-navigation

Updated rspec tests to reflect the expected behaviour

This reverts commit f5201a816f2eff9393e16f362403451e5d86ee6c, reversing
changes made to 48e6db0dad6f256e8423e0bd6c9b254803f50ccf.