Migrate to Volto with plone.volto in upgrade guide needs details

[stevepiercy]

tl;dr: details about how to migrate to Volto from Classic UI are needed. The suggested one-liner in `docs/backend/upgrading/version-specific-migration/migrate-to-volto.md is a good start, but @fredvd offers further details that should be documented in that file.

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I think I can give some more guidance here as well:

"Migrate to richtext" is only concerned with converting (a) richtext field(s) on selected or all content items in your site to the new blocks_layout field in the plone server where all contnt is stored. That's why you can select content types to convert.

But to successfluly migrate your 'ClassicUI' site contents to the default setup that the Plone 6 ReactUI based (Volto) frontend requires, more needs to be done. Such as:

• Activate the plone.volto profile in your site
• Pages and Folders are merged to Folderish pages
• default views are converted by pulling the contents from the default page to the folderish page above
• Convert the Collection content type to a Folderish page with the collection/listing tile in the block layout
• AND convert the richtext fields to blocks layout

As you can see "migrate to volto" does it all, migrate richtext is a part of if. For custom setups, migrate to richtext allows you low level access to this tool .

Why document the 'migate richtext' view? Because if you are an integrator, developer or expert on migration, and don't want/need the default setup with the context type it gives us flexibility in when to process the individual steps.

@FarooqAlaulddin Is this an explanation that gives you more understanding, are there other questions that should be answered specifically to this topic?

@stevepiercy Do you want to update the paragraphs/section involved, or should I suggest an improvement after @FarooqAlaulddin gives his feedback?

Originally posted by @fredvd in #1423 (comment)