When viewing PDF, show a "digitally signed" icon on the top bar

[Extarys]

Is your feature request related to a problem? Please describe.
When viewing PDFs, it might be hard to see that it was digitally signed.

Describe the solution you'd like

Create/add a "universal" icon next to the three dots on the top navbar when the opened PDF has any digital signature, instead

Hovering would show a "This file contains digital signatures, click for more details."
On click, the sidebar could open and show the same details as it would on the "LibreSign" tab when we select the file in Files. See #4164

to avoid people who feel like this would create clutter, add an admin option to show/hide this by default.

Describe alternatives you've considered

Additional context
I saw an issue about the nextcloud pdf viewer, not sure what happened with that, but I cannot open the sidebar from those three dots. 🤷

• Related: Icons part of this reply Add status to LibreSign document at app Files #4160 (comment)

[vitormattos]

Good idea!

Did you have a visual suggestion about the icon? Like a moockup.

About the way to open signature details this suggestion could affect the follow issue:

• Signature metadata not visible when validating a signature #2616
  If we will have a responsible validation page, will be possible load the components of validation page at a right sidebar. Or maybe the icon could open a new modal with validation page over the Viewer or close viewer and open the validation page.

I liked the idea to open at right side, a point to think is how this will work at mobile devices.

[Extarys]

Did you have a visual suggestion about the icon? Like a moockup.

Either the LibreSign logo, or if this is shown for all signed pdf, even the ones not signed by LibreSign, a more generic icon like your signature but in color neutral (white) to fit the other icons :