Feature - More visibility on acknowledged alerts

[lionelwidmer]

The acknowledge feature is very useful to quickly silence an alert is very nice!
However, when combining it with the nice prymitive/kthxbye daemon to automatically extend these silences until the alert is gone from AlertManager, we have the risk to forget about these silences

Proposal: Build a separate view of the silences created using the acknowledge feature (for example using pattern matching (regex pattern matching on the silence comment, based on the pattern defined in config parameter alertAcknowledgement:comment, or an additional filter @Acknowledged, still based on the silence comment pattern matching)
Displaying since when the acknowledgment is active (based on silence creation time), in hours or days, would also be a nice feature to have in the acknowledgment list (by default sorted oldest to newest), in order to identify quickly the acknowledgments that are active since long time