Esteban/686 add defaults in confgs for self service content

[esteban-gs]

686 #685

Goal of PR

Set up the back end functionality to make parts of online hiring configurable by tenant admins - both content and feature flags

Changes:

• Just back-end changes. Config table entries as user-configurable content for online hiring form.
  • There is a mix of app configuration entries - change the app behavior, turn things on/off, etc (feature flags):
  • DisableWorkersVaccineRequirement
  • DisableOnlineOrders
  • And online hiring content - text, links, etc:

        Cfg.OrganizationName,
        Cfg.OrganizationAddress,
        Cfg.WorkCenterDescription,
        Cfg.OnlineOrdersIntroMessage,
        Cfg.OnlineOrdersTerms, // saved as a JSON string and parsed to and from a C# object
        Cfg.OnlineOrdersEnglishReqNote,
        Cfg.OnlineOrdersTransportDetailsLink,
        Cfg.OrderConfirmTransportFeesNotice,
        Cfg.OrderReviewWorkerCountLabel,
        Cfg.OrderReviewSkillsSummaryLabel,
        Cfg.OrderReviewTransportFeeMethodHelper,
        Cfg.OrderReviewLaborCostMethodHelper,
        Cfg.OrderReviewTransportFeeAboutUrl,
        Cfg.OrderReviewLaborCostAboutUrl,
        Cfg.OrderReviewNextStepsHelper,
        Cfg.DisableWorkersVaccineRequirement,
        Cfg.DisableOnlineOrders,
        Cfg.DisableOnlineOrdersBanner,
        Cfg.DisableOnlineOrdersBannerInfoUrl

• Changes in the controller are to validate that users can't change other configs and do delineate user-editable configs vs non
• New view model asp.net attribute to validate the user-editable config keys
• UI not yet implemented on this PR

Alternatives

Another way to set this up is to create a new table Content for all app content that can be configured by the user. Or use a service like Sanity studio