Problem/Motivation
This is a follow-up to #3206643: Project messaging channel in core (as experimental) to give users a way to access the announcements feed if the toolbar module is disabled.
The feed is accessible via the "/admin/announcements_feed" route, but that link is not displayed anywhere if the toolbar module is disabled.
Proposed resolution
Show the link in the following situations:
* The help text provided by the module.
* New link under the "/admin" route.
Remaining tasks
Provide MR.
User interface changes
New "Annoucements" link will appear when viewing the help page and also when going under "/admin".
API changes
None.
Data model changes
None.