FdoSecrets: Improve client executable path handling

[Aetf]

After a busy summer, I'm back with some more time to contribute 😎

This PR improves the overall handling of FdoSecrets showing client executable paths to the user. It does the following

• Check executable file existence as described in [RFC] fdosecrets: add optional confirmation to secret access #4733 (comment)
• Show application PID and dbus address in the client list
• When the executable file is inaccessible, depending on where the client name is shown
  • when shown inline, e.g. in notification text, where space is limited, clearly say that the path is invalid
  • when shown in auth dialog, show warning and print detailed info about the client
  • when shown in the client list, draw a warning icon

More about the auth dialog: someone in previous discussions (sorry I didn't remember exactly where) mentioned showing the process hierarchy. I liked the idea and it looks indeed cool. But I'm not sure if the function belongs to KPXC. Maybe it's better to just let the user use whatever tool already available (e.g. pstree) rather than duplicating the functionality.

Fixes #6459

Screenshots

Client list

Valid exe path

Invalid exe path

Notifications

Auth dialog

When the path is valid, default to collapsed mode

When the path is invalid, default to expanded mode with a warning

Testing strategy

Type of change

• ✅ Bug fix (non-breaking change that fixes an issue)
• ✅ New feature (change that adds functionality)
• ✅ Refactor (significant modification to existing code)

[Aetf]

The windows CI failure is unrelated. And I have no clue why the test fails when building AppImage on GCC in Release mode... probably some random error.

Other than that, this is ready :)

[droidmonkey]

This is some seriously good stuff

[codecov-commenter]

Codecov Report

Merging #6915 (402db68) into develop (860fcfd) will decrease coverage by 0.10%.
The diff coverage is 42.65%.

@@             Coverage Diff             @@
##           develop    #6915      +/-   ##
===========================================
- Coverage    63.78%   63.68%   -0.10%     
===========================================
  Files          330      330              
  Lines        41430    41576     +146     
===========================================
+ Hits         26423    26475      +52     
- Misses       15007    15101      +94     

Impacted Files	Coverage Δ
src/fdosecrets/dbus/DBusMgr.cpp	51.90% <0.00%> (-7.05%)	⬇️
src/fdosecrets/dbus/DBusMgr.h	83.87% <ø> (ø)
src/fdosecrets/widgets/SettingsModels.cpp	44.27% <23.08%> (-7.02%)	⬇️
src/fdosecrets/dbus/DBusClient.cpp	64.95% <31.58%> (-9.41%)	⬇️
src/fdosecrets/widgets/AccessControlDialog.cpp	68.75% <82.09%> (+4.72%)	⬆️
src/fdosecrets/dbus/DBusClient.h	75.00% <83.33%> (+25.00%)	⬆️
src/fdosecrets/objects/Prompt.cpp	74.41% <100.00%> (+0.09%)	⬆️
...rc/fdosecrets/widgets/SettingsWidgetFdoSecrets.cpp	59.02% <100.00%> (+0.45%)	⬆️
src/core/Entry.cpp	83.89% <0.00%> (+0.21%)	⬆️

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