Fallback to JF_ env vars when FJ_ are missing in all cases

[roznawsk]

Acknowledging the stipulations set forth:

• [x] I hereby confirm that a Pull Request involving updates to the Software Development Kit (SDK) has been smoothly merged, currently awaits processing, or is otherwise deemed unnecessary in this context.
• [x] I also affirm that another Pull Request, specifically addressing updates to the documentation body (commonly referred to as 'docs'), has either been successfully incorporated, is in the process of review, or is considered superfluous under the prevailing circumstances.

[codecov[bot]]

Codecov Report

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

Project coverage is 86.92%. Comparing base (7a311a4) to head (3ff7c60). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #199 +/- ## ========================================== - Coverage 87.31% 86.92% -0.39% ========================================== Files 74 74 Lines 1529 1530 +1 ========================================== - Hits 1335 1330 -5 - Misses 194 200 +6 ``` | [Files](https://app.codecov.io/gh/fishjam-dev/fishjam/pull/199?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=fishjam-dev) | Coverage Δ | | |---|---|---| | [lib/jellyfish/config\_reader.ex](https://app.codecov.io/gh/fishjam-dev/fishjam/pull/199?src=pr&el=tree&filepath=lib%2Fjellyfish%2Fconfig_reader.ex&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=fishjam-dev#diff-bGliL2plbGx5ZmlzaC9jb25maWdfcmVhZGVyLmV4) | `95.34% <100.00%> (+0.03%)` | :arrow_up: | ... and [3 files with indirect coverage changes](https://app.codecov.io/gh/fishjam-dev/fishjam/pull/199/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=fishjam-dev) ------ [Continue to review full report in Codecov by Sentry](https://app.codecov.io/gh/fishjam-dev/fishjam/pull/199?dropdown=coverage&src=pr&el=continue&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=fishjam-dev). > **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=fishjam-dev) > `Δ = absolute (impact)`, `ø = not affected`, `? = missing data` > Powered by [Codecov](https://app.codecov.io/gh/fishjam-dev/fishjam/pull/199?dropdown=coverage&src=pr&el=footer&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=fishjam-dev). Last update [7a311a4...3ff7c60](https://app.codecov.io/gh/fishjam-dev/fishjam/pull/199?dropdown=coverage&src=pr&el=lastupdated&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=fishjam-dev). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=fishjam-dev).