feat: add ability to use an existing secret for the myjd service

[pmoscode]

Closes #39

📑 Description

You can now "bring your own secret" for the myjd service.

✅ Checks

• [x] My pull request adheres to the code style of this project
• [x] My code requires changes to the documentation
• [x] I have updated the documentation as required
• [x] All the tests have passed

ℹ Additional Information

[github-actions[bot]]

Test Results

30 tests  +3   30 :white_check_mark: +3   0s :stopwatch: ±0s 17 suites +2    0 :zzz: ±0   1 files   ±0    0 :x: ±0 

Results for commit 42a0fcb7. ± Comparison against base commit f2099d74.

:recycle: This comment has been updated with latest results.