Show message to the user after a successful certificate installation

[MatteoPologruto]

Please check if the PR fulfills these requirements

• The PR has no duplicates (please search among the Pull Requests
  before creating one)
• Tests for the changes have been added (for bug fixes / features)

• What kind of change does this PR introduce?

Enhancement

• What is the new behavior?

A message with infos on the certificate is shown to the user after a successful installation.

• Does this PR introduce a breaking change?

No

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 7 lines in your changes are missing coverage. Please review.

Project coverage is 20.60%. Comparing base (3190a1a) to head (4cf2b6f).

Files	Patch %	Lines
certificates/certificates.go	0.00%	5 Missing ⚠️
systray/systray_real.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #951      +/-   ##
==========================================
- Coverage   20.66%   20.60%   -0.06%     
==========================================
  Files          42       42              
  Lines        2599     2606       +7     
==========================================
  Hits          537      537              
- Misses       1965     1972       +7     
  Partials       97       97              

Flag	Coverage Δ
unit	20.60% <0.00%> (-0.06%)	⬇️

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