Upgrade OpenApiGenerator to v7.16.0 to generate new .NET models/services to support allOf/type, System.Text.Json

[Kwok-he-Chu]

Description

This PR addresses the upgrade of the OpenApiGenerator to v7.16.0 used in the Adyen sdk-automation to generate .NET models & services from the Adyen OpenAPI Specifications. This PR addresses allOf support and native support for System.Text.Json.

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Release notes (WIP)

Added new functionality

Folder-structure

• Introduced a /Core-folder with the following functionality:
  • /Auth contains classes to add authorization to HttpHeaders.
  • /Client contains classes that wrap the ApiResponses and help-functionality to construct the LiveUrl (see UrlBuilderExtensions.cs)
  • /Client/Extensions/ contains the Polly-library that allows user to configure Timeouts, Retries and CircuitBreakers.
  • /Converters contains JsonConverters for DateOnly, DateOnlyNullable, DateTime and DateTimeNullable
  • /Options contains classes to configure the AdyenOptions or AdyenEnvironment (Test/Live).
• All APIs are now part of their own sub-folders
• Support DateTimeOffSet
  • Before: new DateTime(2025, 12, 25, 11, 59, 59)
  • -> After: new DateTimeOffset(2025, 12, 25, 11, 59, 59, TimeSpan.Zero)
• Support DateTimeOnly
  • Before: new DateTime(2025, 12, 25, 11, 59, 59)
  • -> After: new DateOnly(2025, 12, 25)

Mustache templates

• Added api_doc.mustache - Allows documentation generation in /docs folder, only the Service-classes are generated, showing developers how to interact with the API
• Added WebhookHandler.mustache - Allows the WebhookHandler.cs to be generated for deserializing webhooks
• Added modelInnerEnum.mustache, all generated enums are now strings and forward compatible, this fixes Discussion: Should we make the enums forward-compatible? #1071
• Added templates to generate the new models (modelGeneric.mustache) and services (api.mustache), supporting allOf

Changes - Moved classes

• Removed .NET 6.0 in .csproj.
• Moved all TerminalApi classes to the /TerminalApi folder
  • Adyen/Service/TerminalApiAsyncService -> Adyen/**TerminalApi**/Service/TerminalApiService
  • Adyen/Service/TerminalApiSyncService -> Adyen/**TerminalApi**/Service/TerminalSyncService
  • Adyen/Service/TerminalApiLocalService -> Adyen/**TerminalApi**/Service/TerminaLocalService
  • Adyen/Service/TerminalLocalApiUnencrypted -> Adyen/**TerminalApi**/Service/TerminalLocalApiUnencrypted
  • Adyen/Service/TerminalCloudApi -> Adyen/**TerminalApi**/Service/TerminalCloudApi
  • Adyen/Service/TerminalLocalApi -> Adyen/**TerminalApi**/Service/TerminalLocalApi

Breaking changes - Renames

• Renamed & Moved Adyen/Util/HMACValidator.cs -> Adyen/Webhooks/HmacValidatorUtility.

• Removed BalancePlatformWebhookHandler, ClassicPaltformWebhookhandler, ManagementWebhookHandler

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Prerequisites

• Upgraded to .NET 8.0 in this PR.
• Review generated models this branch
• Review and approve this PR for sdk-automation - This contains the pipeline changes & configuration for model/service-generation.
• Review this PR with the changes made to /Core and in the new mustache.templates