Allow usage of global configuration values for TryExamples directive if provided by user

[agriyakhetarpal]

Description

This PR updates the TryExamplesDirective class to use the configuration value in conf.py if specified, and otherwise use the "Try it with JupyterLite" text. This way, buttons that are created manually with the

.. try_examples::

directive in Sphinx will receive the same configuration value, and adding a :button_text input across several .. try_examples:: directives to customise the button text will now not be required. The try_examples_global_button_text string will be used by default, instead of the current "Try it with JupyterLite!" text.

To explain this behaviour, an additional sentence has been added to the documentation for the TryExamples directive page.

Closes #157

Footnotes

This is essentially a breaking change of sorts for dependents who are not using a custom :button_text input already, since it will now change the text to what they have set in try_examples_global_button_text (in case they have set that). But it's surely not a very big change and I would consider it as more of an enhancement (cc: @steppi)

[agriyakhetarpal]

Happy to add a CHANGELOG entry for this if needed!

[agriyakhetarpal]

Oops, let me run black and rebase

[steppi]

Happy to add a CHANGELOG entry for this if needed!

No need! The change log gets autogenerated by the prep release GitHub workflow.

[steppi]

Thanks @agriyakhetarpal! Looking good so far. One thing: I think that all of the global config options should be propagated if a custom option isn't given, not just try_examples_global_button text. You should also do try_examples_global_theme, and try_examples_global_warning_text.

[agriyakhetarpal]

Right, I had thought of doing try_examples_global_warning_text too, but that would become a bigger breaking change, wouldn't it? People will have to override the global warning text and set it to None if they are using manual TryExamples directives somewhere. It does make sense, but I guess you're more aware of how downstream users would react, though.

I agree about try_examples_global_theme, however – I'll make that change and for the other global config options.

[steppi]

Right, I had thought of doing try_examples_global_warning_text too, but that would become a bigger breaking change, wouldn't it? People will have to override the global warning text and set it to None if they are using manual TryExamples directives somewhere. It does make sense, but I guess you're more aware of how downstream users would react, though.

I agree about try_examples_global_theme, however – I'll make that change and for the other global config options.

I think making a breaking change here is fine. jupyterlite_sphinx hasn't hit a stable 1.0 yet and it even says in the docs that try_examples is an experimental directive:

jupyterlite-sphinx/docs/directives/try_examples.md

Lines 3 to 4 in a0903f5

	`jupyterlite-sphinx` provides the experimental `try_examples` directive which allows
	docstring examples sections written in [doctest format](https://docs.python.org/3/library/doctest.html) to be swapped with an embedded classic Notebook at the push of a button.

It would be surprising to me if some global config options were respected for manually inserted directives but not others. Since we're working with an experimental directive, we can make breaking changes to ensure consistent behavior. I think the default for global warning text is that there should be none. If someone sets a global warning text, and wants to override it in a few places, then I don't think it's a big deal for them to have to manually set the warning text to None for those specific instances.

[agriyakhetarpal]

Fair point, didn't consider that the directive was/is still experimental – I have added in the requested changes! Now, one should be able to use the global warning text and use the global name for the theme/CSS container styling.

[steppi]

Thanks @agriyakhetarpal. This is looking better. A few minor suggestions.

[steppi]

Thanks @agriyakhetarpal. this is in good shape now. Just a couple minor suggestions on language.

[steppi]

Thanks @agriyakhetarpal! This looks good now.