Add an option to combine all architectures into one tags table in generated readmes

[lbussell]

The latest dotnet/samples tags tables are identical between the 3 supported Linux architectures: https://github.com/dotnet/dotnet-docker/blob/96825a00cf9f25c2404337f9785ec1d84d030d86/README.samples.md#full-tag-listing

This is because we undocumented the arch-specific tags since they didn't provide much value for the samples use cases.

Since all of the tables are the same, they are redundant. We should provide some mechanism to combine them all into one table. It could be automatic, or perhaps an extra option in the manifest.

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[lbussell]

[Triage] There is limited ROI for this change since it only affects the samples images. It would also add additional complexity to the readme generation and make the tags tables less consistent across repos.

We can consider revisiting this/opening another issue once more of the appliance image repos (monitor, aspire dashboard) have tags tables that look similar to this.