Change new nav purple to indigo

What does this MR do?

Port of gitlab-ce!12684 to EE

Does this MR meet the acceptance criteria?

• Tests
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/34402

marked the checklist item Branch has no merge conflicts with master (if it does - rebase it please) as completed

changed the description

marked the checklist item Squashed related commits together as completed

marked the checklist item Conform by the style guides as completed

changed the description

marked the checklist item Conform by the merge request performance guides as completed

assigned to @iamphill

assigned to @annabeldunstone

LGTM! Thanks @pedroms

approved this merge request

merged

mentioned in commit 30345c81