Cleanup plot_with_settings namespaces names

[m7pr]

Feature description

If you grep for teal.widgets::plot_with_settings_ui you can see a discrepancy in naming convention for the plot namespaces.
In half of the examples we have meaningful names but in other half we have just myplot.

I suggest we unify, and either put the same name everywhere, or use custom meaningful names in all modules.
If we decide to stick with the same name all over the modules, I would suggest using plot instead of myplot.

Those names are used further in the name of the element of the page when shiny app is running, hence it's used in automated testing.

I suggest we also do that in other packages, below is the result for {teal.modules.clinical}.