Add danger rule for text-secondary CSS class
What does this MR do?
Stop people adding text-secondary
class. Its computed value is set in a complex and terrible way (our bootstrap vars import order is wrong) - #225622 (closed).
It is also overridden by sourcegraph styles when used on the MR page - #228785 This is particularly noticeable in dark mode - #228752 (closed)
For all these reasons, and more, it should be avoided.
Disclaimer: I have no idea what I'm doing and the addition is based on copypaste of the eslint dangerfile