Rewrite release instructions for the branch-based release process

[rockfordlhotka]

Closes #4940

Rewrites docs/dev/Create-a-CSLA-.NET-release.md to describe how releases work now, as used for 10.2.0:

• Pushing release/vX.Y.Z publishes the core packages, and release-maui/vX.Y.Z publishes Csla.Maui. Both runs need approval in the nuget-release environment and use NuGet trusted publishing, so no API key is stored.
• Which branch to release from (main for CSLA 11, v10.x for CSLA 10).
• Step by step: release notes, the version change PR, the core release, waiting for nuget.org to index the packages, pointing Csla.Maui and the samples at the released version, the MAUI release, the GitHub release and tag, unlisting superseded prereleases, and cleanup.
• Prereleases and troubleshooting.

Removed: the local Windows, .NET 8/9 SDK and Visual Studio prerequisites, and the local dotnet pack plus push-nuget-packages.sh steps. That script is now mentioned only as a manual fallback.

A matching PR into v10.x follows.

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