Dashboard Module: Show link to manage existing nodes of specific content type

Description of the need I think it's not always clear to a site editor how to use the available filters on the manage content page (admin/content) or that users don't necessarily think about this option. It would be nice to give site editors a really simple way to see a list of existing nodes of a specific content type, without having to first figure out the filters on the manage content page.

Proposed solution Since we now have such a cool dashboard and have added a create new link for each content type there, I'd like to propose altering this block a little to also add a manage existing nodes links. All it does is take the user to the existing "manage content" page, but with the filter preset for the content type of their choice.

Existing block:

Proposed block:

Alternatives that have been considered

I already added this block to the Dashboard Plus module and we certainly could give it some time for users to test it and see if they like it. However, since the work has already been done and it is in my opinion a clear improvement to the current block, with little to no downside, I'd like to see what others think about adding it to core sooner rather than later.

Feature request for Dashboard Plus: https://github.com/backdrop-contrib/dashboard_plus/issues/4

Additional information

The "manage content" link in the footer of the block is redundant with a similar link in the "content overview" block. It could be removed or left there in case the block gets moved or used in other contexts.

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PR by @stpaultim: https://github.com/backdrop/backdrop/pull/2795