Y24-375 scRNA - refactored shared constants to move them into a central config file

[andrewsparkes]

Closes #1983

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 71.42857% with 2 lines in your changes missing coverage. Please review.

Project coverage is 78.20%. Comparing base (785f323) to head (1166fc6). Report is 45 commits behind head on develop.

Files with missing lines	Patch %	Lines
...s/validators/required_number_of_cells_validator.rb	60.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #2050 +/- ## =========================================== + Coverage 77.91% 78.20% +0.28% =========================================== Files 463 471 +8 Lines 17720 18226 +506 Branches 225 262 +37 =========================================== + Hits 13807 14253 +446 - Misses 3911 3971 +60 Partials 2 2 ``` | [Flag](https://app.codecov.io/gh/sanger/limber/pull/2050/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=sanger) | Coverage Δ | | |---|---|---| | [javascript](https://app.codecov.io/gh/sanger/limber/pull/2050/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=sanger) | `70.43% <ø> (+0.83%)` | :arrow_up: | | [pull_request](https://app.codecov.io/gh/sanger/limber/pull/2050/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=sanger) | `77.97% <71.42%> (+0.05%)` | :arrow_up: | | [push](https://app.codecov.io/gh/sanger/limber/pull/2050/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=sanger) | `77.90% <71.42%> (-0.02%)` | :arrow_down: | | [ruby](https://app.codecov.io/gh/sanger/limber/pull/2050/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=sanger) | `91.13% <71.42%> (-0.03%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=sanger#carryforward-flags-in-the-pull-request-comment) to find out more.

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[andrewsparkes]

@KatyTaylor I think the idea is to remove the current functionality that allows a study override for required_number_of_cells_per_sample_in_pool. This would mean this validator is no longer required: app/models/validators/required_number_of_cells_validator.rb In this PR I have just removed usage of the override in the export files. Removal of the validator should be another small story I think. It's intertwined with the presenter code so not straight forward.