--showlocals should be overridable, e.g. #10381

What's the problem this feature will solve?

• Assume addopts is globally set to have --showlocals
• It's not possible for py.test invocations to override the option on one-off invocations / pytest steps in CI workflows

Describe the solution you'd like

--showlocals=false or --no-showlocals / --without-locals

Alternative Solutions

Open to hearing others

Additional context

Mentioned earlier here: #8974 (comment)

This differs from #8974 in:

• being narrowly tailored solution wise - allow an argument to negate the locals showing
• has a technical solution that can be addressed directly PR'd if maintainers willing