Consider not adding the wrapper to all blocks by default

[sneridagh]

Volto 18 (and 17) already have the core stylewrapper which lead to have duplicated wrappers, with the same classnames:

This could lead to conflictive CSS declarations because of the nested stylewrapper in blocks that really don't use this add-on.

We had in fact, this situation:
We installed @eeacms/volto-tabs-block, inadvertently it installed @eeacms/volto-block-style.
Then all our blocks had all of a sudden an extra stylewrapper coming apparently "from nowhere".

I know, it's on the README in bold, but still I won't have expected that this will happen. I'd expect that it only applies to the blocks that use it.

The workaround is to use the pluggableStylesBlocksWhitelist or pluggableStylesBlocksBlacklist to specify the blocks that we want to mark, but it's not documented in the README. However, this has a drawback in itself, if you use the new setup, since if you are using the addons of your policy package, the setting is being applied afterwards @eeacms/volto-block-style config kicks-in. The workaround is to specify the addon in volto.config.js instead, but it's kind of cumbersome and not portable anymore...

const addons = ['volto-my-policy-addon', '@eeacms/volto-tabs-block'];
const theme = '@kitconcept/volto-light-theme';

module.exports = {
  addons,
  theme,
};