Pass string value in through haml template data attribute
Evaluate it into a regex when initiating variable list
Use it to determine whether to show the maskability warning

Set the default value to false
Adjust tests to expect false as the default
Update documentation to make new default clear

In addition to API, add support for toggling mased on UI too.

(Though fabricate_via_browser_ui is private)

Adds custom-select class to the select menu for variables
type in CI/CD settings

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

Add env_var and file as supported types for CI variables. Variables of
type file expose to users existing gitlab-runner behaviour - save
variable value into a temp file and set the path to this file in an ENV
var named after the variable key.

Resolves https://gitlab.com/gitlab-org/gitlab-ce/issues/46806.

Update error message "This variable will not be masked" to
"Cannot use Masked Variable with current value"
Add link to masked variables section to error message

Makes changes for truncation and combines the two related CSS classes.
Applies new tooltip comp as close as possible to the span for testing.