#5999 Add fingerprint when rendering private backups

[martgil]

This PR adds the key's fingerprint when rendering the private key backups in Gmail for easier recognition of keys, useful when removing unnecessary keys permanently.

Closes #5999

Screenshots:

For already imported keys:

For unimported keys:

---

Tests (delete all except exactly one):

• Does not need tests (refactor only, docs or internal changes)

---

To be filled by reviewers

I have reviewed that this PR... (tick whichever items you personally focused on during this review):

• addresses the issue it closes (if any)
• code is readable and understandable
• is accompanied with tests, or tests are not needed
• is free of vulnerabilities
• is documented clearly and usefully, or doesn't need documentation

[martgil]

Hi @sosnovsky, this one is ready for a review. thank you!

[sosnovsky]

works well 👍