Update UI text in locked and confidential warnings

Background

When a work item or legacy issue is locked and/or confidential, a warning is shown above the comment form indicating the limited participation or visibility. This today uses the item type, which is failing on Incidents resulting in awkward phrasing e.g. "This is a confidential ." Injecting type names can also lead to i18n challenges in cases where the surrounding phrasing doesn't always match the type name, such as if the surrounding language expects a masculine noun but the type name is feminine in a language with grammatical gender.

Additionally

• Now that we support locking discussion in epics, we need to account for the fact that epics are in groups and not projects, rather than saying "project members".
• Current link from "Learn more" on confidential issues points to wrong docs page (Confidential OKRs)

Proposal

Case	Current	Updated
Confidential	This is a confidential %{noteableTypeText}. People without permission will never get a notification.	This is marked as confidential. People without permission will never get a notification.
Locked	The discussion in this %{noteableTypeText} is locked. Only project members can comment.	This discussion is locked. Only members can comment.
Both	This %{noteableTypeText} is %{confidentialLinkStart}confidential%{confidentialLinkEnd} and its %{lockedLinkStart}discussion is locked%{lockedLinkEnd}. People without permission will never get a notification and won't be able to comment.	This is %{confidentialLinkStart}marked as confidential%{confidentialLinkEnd} and its %{lockedLinkStart}discussion is locked%{lockedLinkEnd}. People without permission will never get a notification and won't be able to comment.