be shown to users when using that provider
This can be used to return a translated warning message which should be
shown to users of this provider. It's intended for use in cases such as
a provider which relies on a 3rd-party backend, where the version of the
backend software is not officially supported, or for alerting users to
providers in a "beta" or "untrustworthy" state.
For the c++ api dox this expands to "\c nullptr" (the
\c directive indicates a code literal value), and for sipify/Python
it expands to ``None`` (`` is sphinx annotation for literal values)
Makes for nicer dox for both c++ and Python!
And require that showing help is opt-in. Apart from a handful
of built-in providers, most providers will not have help pages
available within the QGIS documentation (including model and
script algorithms). Accordingly, we should hide the help button
by default and only show it for these selected providers.
Note that 3rd party algorithms can still specify custom helpUrl
urls, in which case the button WILL be shown.
