[Feedback needed] Add --suite-load-timeout option

[nilsreichardt]

This PR adds a --suite-load-timeout argument to remove the hard-coded timeout (see #2463). [More description is added later]

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[nilsreichardt]

@natebosch I need a bit of feedback here. Would be a --suite-load-timeout option a good solution for this? Should we use a different name?

If you are not the right person for this, could you tag someone else?

After this, I will add tests for this PR 👍

[nilsreichardt]

I implemented --suite-load-timeout the same way as --ignore-timeouts was implemented. However, it's not optimal that we have two locations for the default value. Here and in pkgs/test_core/lib/src/runner/configuration/args.dart. Should we improve this? Or not? Or just writing a comment to update the default value also in the other file?