"Hide" HTML support from API

[oskogstad]

Introduction

This removes the support for HTML in additionalInfo and other content properties

Description

In order to support rich content, a subset of HTML has been allowed in additionalInfo. Frontchannel embeds, which should be used for most content payloads/text bodies, will only support markdown (CommonMark flavour).

HTML is intrinsically a markup language that allows for definition of layout, not just rich content. This is in contrast to markdown, which is designed to allow for definition of rich content only. Supporting HTML has challenges related to eg. nesting of tags, which makes it harder to control how rich content is placed within a layout.

Supporting only markdown makes it easier to preserve desired layout, whilst providing fairly rich facilities for text formatting. Note that CommonMark specification will not be supported in full; some features might not be supported or in other ways constrained in order to maintain layout/responsitivy, eg. tables.

For migration purposes however, HTML support will have to be supported. Use of HTML for these scenarios will require an additional oauth scope to be present.

See also #329

Implementation

If there are guidelines on architecture or other implementation choices, they are added here. Different approaches can also be discussed here.

Tasks

Beta Give feedback

1. Implementation tasks are added here
2. Prepare documentation (if relevant - either update working document, or add a new file in docs)
3. Add e2e-test (if relevant)

[TheKnarf]

• Altinn 2 migration team should get their own scope
• Drop html support in additionalInfo
• Only support html for alltinn 2 scope in embaddable content
• Name the media type for embeddable content something like "altinn2-migration-legacy-html"
• Create a PDF with documentation specifically for the Altinn 2 migration team (they requested some additional documentation, and this doesn't need to be public, but only for their team)