Replace deprecated openpgp library

[umbynos]

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?

Dependency replace

• What is the current behavior?

The openpgp library we were using has been marked as deprecated (see golang/go#44226)

• What is the new behavior?

Replace it with a maintaned one

• Does this PR introduce a breaking change?

no

• Other information:

Similar to arduino/arduino-cli#2333
Has to be rebased on main after #838 is merged

[codecov-commenter]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (3f05681) 18.90% compared to head (a4c86c4) 18.90%.

Additional details and impacted files

@@                     Coverage Diff                     @@
##           remove-indexes-v2-endpoint     #839   +/-   ##
===========================================================
  Coverage                       18.90%   18.90%           
===========================================================
  Files                              46       46           
  Lines                            3624     3624           
===========================================================
  Hits                              685      685           
  Misses                           2849     2849           
  Partials                           90       90           

Flag	Coverage Δ
unit	18.90% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
index/index.go	52.50% <100.00%> (ø)

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