feat(Extension): use signed git commits

[maxpatiiuk]

Commit signing might be useful in some advanced use cases (when the text hoarder store is set to a multi-user repository), but it would require 3 network requests for each commit rather than 1, and complicate the code.

Thus, this is a no-go for the time being, but keeping this issue open just for reference

docs: https://github.com/orgs/community/discussions/50055