Update dependabot config to use `directories`

[gewarren]

See https://github.blog/changelog/2024-06-25-simplified-dependabot-yml-configuration-with-multi-directory-key-directories-and-wildcard-glob-support/. This should result in fewer dependabot PRs and we can also remove the dependabot-bot workflow.

• dotnet/docs
• dotnet/dotnet-api-docs
• dotnet/dotnetfw-api-docs
• dotnet/dotnet-api-docs-temp
• dotnet/docs-desktop
• dotnet/aspnetcore.docs
• dotnet/docs-maui
• dotnet/docs-mobile
• dotnet/docs-archive-pr
• dotnet/docs-tools
• dotnet/docs-actions
• ...

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Associated WorkItem - 633904