Show for how long a "sticky" notification has been displayed

[Poslovitch]

Describe the problem to be solved

Sticky notifications were introduced in #3347. There is, however, no way to know when it was displayed. This information could be considered helpful in cases where the user encounters an error (be it uploading a video, modifying settings, etc.) and additional information (such as logs) would be available on the server (thus helping to sift through the logs).

Describe the solution you would like:

I suggest adding something like 'X time ago' on these sticky notifications. Something similar to what's already done on notifications:

Maybe taking inspiration from Bootstrap?

Also, providing the exact date and time when hovering the "x time ago" text would be helpful:

[Poslovitch]

I was able to implement such a feature. However, there's an issue (don't mind the CSS, haven't done it yet):

The text will never update, and therefore remain as "just now" no matter how long the toast's been displayed. Has someone got any hints or workarounds that I could try to get this problem out of the picture?

Based on what I've seen, toasts are handled by PrimeNG: they provide the p-toast component which we then populate with the content we want.
I'm not sure what kind of "control" over the component this gives us. Are we allowed to override/overwrite some of its functions? (would it even be useful?)

I think that running a function every X seconds would be a very stupid idea. That would work, but oh boy that'd be stupid.

[Poslovitch]

My current implementation can be seen at https://github.com/Poslovitch/PeerTube/tree/feature/3395-toast-x-time-ago