Consolidate Kontent .NET repositories into a single repo

[petrsvihlik]

Motivation

Basically, the same as Microsoft's. Mainly:

• PRs spanning multiple repos.

More details at:

• Consolidating .NET GitHub repos dotnet/announcements#119
• Migrating dotnet/extensions content to dotnet/runtime and dotnet/aspnetcore aspnet/Announcements#411

Proposed solution

Merge repos that are tightly dependent on each other:

• kontent-delivery-sdk-net
• kontent-management-sdk-net
• kontent-generators-net - keep as single rep and have a switch for MAPI - keep contentmanagementapi
• kontent-aspnetcore

into a single repo.

Additional context

Additionally, we want to:

• preserve the git history
• utilize CODEOWNERS scopes to distribute the responsibilities among the teams
• consolidate the build definition and keep it in the YAML files only
• consolidate the READMEs, wikis, and docs and rethink their structure
• consolidate the URL generation (Move Kentico.Kontent.Delivery.Urls.QueryParameters to .Abstractions #241)
• migrate (and revisit+label) all issues
• archive (but not delete) the old repos (to keep SourceLink functional)
• TODO: version management (simple: always release all packages with the same version, complex: keep the versioning of the packages independent)
• Think about namespaces best practices: Namespace unifications #300

This is a pre-requisite to: #241

[petrsvihlik]

@Simply007 This could help you manage DevOps on a larger scale too: https://github.blog/2021-11-29-github-actions-reusable-workflows-is-generally-available/