Re-add DUO to our docs

Problem to solve

We previously removed references to DUO 2FA from our docs because the implementation efforts are still ongoing. After support for DUO is implemented we should re-add DUO to our docs.

Other links/references

• MR for DUO implementation: !90564 (closed)
• Issue about DUO support: #15760 (closed)
• MR where DUO was removed: !104093 (merged)
• MR with the changes to re-add to DUO in our docs: !109323 (closed)