Evaluate the symfony/config dev dependency

[TravisCarden]

• Part of https://github.com/php-tuf/composer-stager/issues/78.

Dependency	symfony/config
Description	Helps you find, load, combine, autofill and validate configuration values of any kind.
Value/justification	Indispensable. This is used for service autoloading in tests, which is not only convenient but actually exercises the API as it would be used by clients.
Usage/popularity	Extremely high. Currently over 225M installs and 5K dependents on Packagist.
Security policy	https://github.com/symfony/config/security/policy
Maintainance	The maintenance details for all Symfony components are the same and have already been evaluated for inclusion of others in Drupal core.
Considerations	Drupal core may already be going to add symfony/config to its own dependencies: Use native Symfony YamlLoader + Config [#3111008] Could possibly be eliminated by converting the services configuration to XML, if desirable.

Dependency tree

$ composer info --tree symfony/config
symfony/config v6.2.7 Helps you find, load, combine, autofill and validate configuration values of any kind
|--php >=8.1
|--symfony/deprecation-contracts ^2.1|^3
|  `--php >=8.1
|--symfony/filesystem ^5.4|^6.0
|  |--php >=8.1
|  |--symfony/polyfill-ctype ~1.8
|  |  `--php >=7.1
|  `--symfony/polyfill-mbstring ~1.8
|     `--php >=7.1
`--symfony/polyfill-ctype ~1.8
   `--php >=7.1

[effulgentsia]

I think it's quite sensible to leave symfony/config as a dev dependency of Composer Stager.

Drupal core may already be going to add symfony/config to its own dependencies. (Citation?)

https://www.drupal.org/project/drupal/issues/3111008 is the issue for that. That issue still has challenges to work through, but that's related to using symfony/config at runtime and reconciling the remaining differences between how Symfony builds the service container vs. how Drupal currently builds it. But none of those concerns are reasons to not use symfony/config as a dev dependency of this package.