Adds ENV vars for configuring the BB server

[microstudi]

fixes #287 supersedes #301

[codecov-commenter]

Codecov Report

Attention: 5 lines in your changes are missing coverage. Please review.

Comparison is base (6e0a171) 69.57% compared to head (a6818dc) 69.57%.

Files	Patch %	Lines
...letin_board/server/app/graphql/types/query_type.rb	66.66%	3 Missing :warning:
...r/app/commands/sandbox/generate_load_test_stats.rb	0.00%	1 Missing :warning:
...oard/server/app/jobs/sandbox/generate_votes_job.rb	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #310 +/- ## ======================================== Coverage 69.57% 69.57% ======================================== Files 96 96 Lines 1630 1630 ======================================== Hits 1134 1134 Misses 496 496 ```

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[andreslucena]

@microstudi there's a failing spec, can you check it out please?

[microstudi]

All done @andreslucena !