Feature/manually add api key

[acoumb]

Current PR contains the implementation of a feature allowing administrators to persist an API key in the database. With this update, as a service could have a key both in the settings and in the database, across various checks the stored token takes precedence.

Updates:

• CanManuallyProvideApiKey property for service detail, to toggle visibility of the Add API key section in the backoffice.
• Storage implementation using IKeyStorage.
• Migration
• Methods for persisting the API key.
• Unit tests

[acoumb]

Updates look good. My plan was to first have the additional authorization flows finished and merged into develop, and handle docs related tasks in separated PRs.

Merging this for now and we can discuss more in our meeting.