V15: Allows certain adjustments of the logo

[iOvergaard]

This pull request includes several changes to the src/Umbraco.Web.UI.Client and src/Umbraco.Web.UI.Login directories, focusing on the app-logo.element.ts, backoffice-header-logo.element.ts, and auth-layout.element.ts files. The changes enhance the flexibility and customization of logo elements and improve code consistency.

This should resolve #18424

Changes

• Made the app-logo component listen for the active theme and select logo based on that
• Added more options to the app-logo element to override the theme and lazyload or not
• Added new alternative logo (the blue logomark) as an option in the backoffice, although it is not being used anywhere in the core UI, but this ensures we are consistent with the login logo, which has two versions
• Optimised the logo SVG files to remove unneeded metadata
• Added more CSS variables to control the dimensions of the logo and documented them
• Added appropriate mock handlers for the new logo

Enhancements to Logo Elements:

This pull request introduces support for an alternative backoffice logo, along with various updates to the logo handling in the application. The changes span across multiple files, including controllers, configurations, UI components, and mock handlers.

Addition of Alternative Backoffice Logo:

• src/Umbraco.Cms.Api.Management/Controllers/Security/BackOfficeGraphicsController.cs: Added a new route LogoAlternativeRouteName and a corresponding method LogoAlternative to handle requests for the alternative backoffice logo. [1] [2]

• src/Umbraco.Core/Configuration/Models/ContentSettings.cs: Introduced a new property BackOfficeLogoAlternative to store the path to the alternative backoffice logo. [1] [2]

Updates to UI Components:

• src/Umbraco.Web.UI.Client/src/apps/app/app-logo.element.ts: Enhanced the UmbAppLogoElement component to support loading attributes, logo types, and theme overrides. Updated the rendering logic to select the appropriate logo based on the theme and logo type. [1] [2]

• src/Umbraco.Web.UI.Client/src/apps/backoffice/components/backoffice-header-logo.element.ts: Modified the UmbBackofficeHeaderLogoElement to use the updated UmbAppLogoElement with the new properties and removed redundant context consumption. [1] [2] [3] [4] [5]

• src/Umbraco.Web.UI.Login/src/components/layouts/auth-layout.element.ts: Added CSS properties for customizing the logo display and updated the rendering logic for the logo images. [1] [2] [3] [4] [5]