[Feature]: Introduce FactorySettings

[chaen]

User Story

Currently, there are a lot of:

• hardcoded environment variables (DIRACX_CONFIG_BACKEND_URL, DIRACX_LEGACY_EXCHANGE_HASHED_API_KEY)
• Dynamically generated variables based on entrypoints ( DIRACX_DB_URL_*, DIRACX_SERVICE_*_ENABLED`)

It's messy, and easy to introduce bug

Feature Description

Introduce a FactorySettings class that would:

• group together all these hardocded variable
• explore the entrypoints to generate the DB/ENABLED

Definition of Done

No response

Alternatives Considered

No response

Related Issues

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Additional Context

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