Use config object in Dataset controller

Summary

Currently in datasets controller, we retrieve the values for the following variable directly from process.env:

• CREATE_DATASET_WITH_PID_GROUPS
• DATASET_CREATION_VALIDATION_ENABLED
• DATASET_CREATION_VALIDATION_REGEX
• ADMIN_GROUPS

For consistency sake, we should use the config object, which use the env variables, but also allows a facility to further customize the configuration directly in code if env variables are not enough for their use case.

Expected Behaviour

datasets.controller import config object and use equivalent values in there.
Config object pulls in the equivalent env variable value if they are configured, or use the default one hardcoded.

Extra Details

Changes in Dataset.controller should be done at the following location:

• https://github.com/SciCatProject/scicat-backend-next/blob/a9ac0adaec026204dae501366106d23ed288163d/src/datasets/datasets.controller.ts#L213
• https://github.com/SciCatProject/scicat-backend-next/blob/a9ac0adaec026204dae501366106d23ed288163d/src/datasets/datasets.controller.ts#L219
• https://github.com/SciCatProject/scicat-backend-next/blob/a9ac0adaec026204dae501366106d23ed288163d/src/datasets/datasets.controller.ts#L219
• https://github.com/SciCatProject/scicat-backend-next/blob/a9ac0adaec026204dae501366106d23ed288163d/src/datasets/datasets.controller.ts#L283

Start in src/datasets/datasets.controller.ts at the referenced lines and inspect the existing config object for equivalents of the four process.env variables: CREATE_DATASET_WITH_PID_GROUPS, DATASET_CREATION_VALIDATION_ENABLED, DATASET_CREATION_VALIDATION_REGEX, and ADMIN_GROUPS. Update the controller to use those config values, preserving configured environment values and defaults; done means no direct environment reads remain for these settings.