Regexp log search, results date interval and count

[DavidePrincipi]

The System logs page Search matches by a simple substring. 🤔 When the Search completes, it's not clear if the Max lines limit was reached or not, and what is the time interval the returned lines cover.

1. 🎯 Enable search by regular-expression
2. 🎯 Show the number of retrieved log lines and their date-time interval

---