Add OTP capabilities

[adur1990]

Summary

With the [pass otp](https://github.com/tadfisher/pass-otp) extension, it would be nice to automatically fill the OTP code on request.

Motivation

It somewhat annoying to have Pass for macOS fill the passwords nicely but than you have to switch to the terminal anyway to fill the OTP.

[dtrainych]

hi @adur1990 , than you for this great app and extension. I don't know about automatically fill the otp code, as it can be hard to identify the field on web page and require additional key combination or click for user.
In my opinion pass for iOS implanted ideal solution, where after the username and password is filled, OTP code is copied to clipboard, so the user needs only to paste it.
Sadly, I don't have experience with swift. But if you point me the part where this new code should be added, I could try to implement it.