Add `gl-focus-outline-none:focus` utility class

Problem to solve

The GitLab application has several instances of Bootstrap Vue's bv-no-focus-ring class.

GitLab issue: gitlab#296949 (closed)

Proposed solution

Add a new utility class to replicate bv-no-focus-ring's style.

.bv-no-focus-ring:focus {
  outline: none;
}

.gl-focus-outline-none:focus {
  outline: none;
}