Support configuration of subform layoutset with allowed components only

[framitdavid]

Problem Statement
As a service developer, I need the ability to configure a subform's layout set to include only the components that are allowed and within the subform context.

Restrictions for unsupported components:

• File Upload: FileUpload components should not be allowed in subforms.
• Submit Button with processNext: A "submit button" that triggers processNext should be excluded from subforms, as subforms cannot navigate to the next step.
• SubForm: SubForm should not be possible to add within a SubForm layoutset

[framitdavid]

Could be solved the same way as payment layoutset.

[framitdavid]

This issue is closed until https://github.com/Altinn/altinn-studio/issues/13479 is done. ✅

[ErlingHauan]

Adding some more information from Slack:

Eksempler på ting man ikke kan ha i layouten for et underskjema

• Knapper som kjører process/next, det vil si vår vanlige Button, men også ActionButton
• Kanskje åpenbart, men ikke InstantiationButton. Usikker på om Studio støtter den fullt ut heller, men det er en knapp man bare burde kunne ha i et stateless-steg.
• Usikker, men siden et underskjema ikke er et eget steg, vil jeg jo tenke at Payment-komponenten ikke gir mening å ha der.
• Filopplastning slenger nå en runtime error spesifikt hvis den brukes i underskjema
• Også verdt å nevne at CustomButton actions som kaller process/next vil også feile