Migrate dev-specific configuration to env vars via .env file

[acelaya]

Closes #2221

This PR updates how dev/local configuration is handled by Shlink, to use env vars defined in env-specific files rather than local configuration files that overwrite global ones.

• Try to define all local/dev config via env vars and get rid of .local config files
• Stop using Valinor factories
• Consider defining dev env vars as a PHP array and load them via loadEnvVarsFromConfig.
• Update CONTRIBUTING documentation
• Add ADR explaining why this approach is taking

[codecov]

Codecov Report

Attention: Patch coverage is 30.83333% with 83 lines in your changes missing coverage. Please review.

Project coverage is 93.50%. Comparing base (5fb6c87) to head (8486053).
Report is 17 commits behind head on develop.

Files with missing lines	Patch %	Lines
...le/Core/src/Config/Options/UrlShortenerOptions.php	20.00%	16 Missing ⚠️
module/Core/src/Config/Options/QrCodeOptions.php	0.00%	12 Missing ⚠️
module/Core/src/Config/Options/TrackingOptions.php	35.29%	11 Missing ⚠️
module/Core/src/Config/Options/RobotsOptions.php	22.22%	7 Missing ⚠️
module/Core/src/Matomo/MatomoOptions.php	0.00%	7 Missing ⚠️
module/Core/src/Config/EnvVars.php	14.28%	6 Missing ⚠️
...Core/src/Config/Options/DeleteShortUrlsOptions.php	25.00%	6 Missing ⚠️
...ore/src/Config/Options/NotFoundRedirectOptions.php	0.00%	6 Missing ⚠️
module/Core/src/Config/Options/AppOptions.php	28.57%	5 Missing ⚠️
module/Core/src/Config/Options/RedirectOptions.php	0.00%	5 Missing ⚠️
... and 1 more

Additional details and impacted files

@@              Coverage Diff              @@
##             develop    #2224      +/-   ##
=============================================
- Coverage      94.84%   93.50%   -1.34%     
- Complexity      1592     1607      +15     
=============================================
  Files            270      270              
  Lines           5527     5608      +81     
=============================================
+ Hits            5242     5244       +2     
- Misses           285      364      +79     

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