Add the 1Password CLI as a custom backend

[jeliebig]

What this PR does / why we need it:

This PR adds the 1Password CLI as an additional custom backend.

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #424

Special notes for your reviewer:

I really wanted to make the tests work as well, but for some reason op always thinks it is not authenticated. Manually running the decrypt function with the test file does work as expected. I tried a few things to make this work with BATS:

• The configuration directory for op ~/.config/op was copied to ${HOME}/.config/op within setup_suite.bash
• Additionally I tried to add a session token via an exported env var or using the --session parameter of op
• Trying to authenticate op within setup_suite.bash doesn't work, since op reports it is not signed in during the test run anyway

If you don't have an idea on how to potentially fix this and don't want to keep some manual test instructions for this I'll remove that commit again.

PR Readiness Checklist:

Complete these before marking the PR as ready to review:

• [x] the CHANGELOG.md release notes have been updated to reflect any significant (and particularly user-facing) changes introduced by this PR

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (402de1e) 86.56% compared to head (7f90153) 86.56%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #431 +/- ## ======================================= Coverage 86.56% 86.56% ======================================= Files 23 23 Lines 856 856 ======================================= Hits 741 741 Misses 115 115 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[bilby91]

Looking forward to testing the feature!

[jkroepke]

At the moment, I have no clue, why IT tests with coverage are failing.

[jeliebig]

At the moment, I have no clue, why IT tests with coverage are failing.

Could that be caused by me changing things in the test libraries?

[jeliebig]

Hmmm, now it seems there is a problem with uploading a new report?